ALOS (Advanced Land Observing Satellite) / Daichi
ALOS (Advanced Land Observing Satellite) / Daichi
ALOS (nicknamed ”Daichi”) is a Japanese Earth-observation satellite, developed by JAXA (Japan Aerospace Exploration Agency, Tokyo; formerly NASDA), and manufactured by NEC, Toshiba, and Mitsubishi Electric Corp. The objectives call for an optical and an active microwave sensor payload who's high-resolution data may be used for such applications as cartographic mapping, environmental and hazard monitoring (within 48 hours). The intent is to provide the user community with data of sufficient resolution to be able to generate 1:25,000 scale maps. This in turn requires observational data of 2.5 m horizontal resolution for the determination of land conditions, and a 3-5 m vertical accuracy for contour mapping. Multispectral data with 10 m horizontal resolution is needed for the classification of land cover (vegetation, forests, etc.). Short-term hazard monitoring (within 24 hours on average) will be accommodated by the use of pointing mechanisms. Particular application features of the ALOS mission are: 1) 2) 3)
• The mapping of land areas (without the need for ground control points) for cartographic applications
• The monitoring of disasters on a global scale (as a complement to the capabilities of other spacecraft) 4)
• Resource surveying.
The S/C structure consists of CFRP (Carbon Fiber Reinforced Plastic) trusses and aluminum fittings. The approximate S/C dimensions in the stowed configuration are: 6.4 m x 3.4 m x 4.3 m (x, y, z); the in-orbit configuration dimensions are: 8.9 m x 27.4 m x 6.2 m (x, y, z, where x is in the velocity direction and z is toward nadir).
Figure 1: Schematic illustration of the ALOS spacecraft (image credit: JAXA)
The S/C mass is about 4000 kg (at lift-off, 180 kg of hydrazine), the largest satellite ever for Japan. Its solar array (size 22 m x 3 m) generates power of 7 kW (EOL). ALOS has five sets of NiCd type battery (BAT). On orbit, a paddle drive rotates the solar array into the sun for maximum efficiency. A combination of active/passive thermal control subsystem is used. The spacecraft design life is 3 years with a goal of 5 years.
AOCS (Attitude Orbit and Control System): The ALOS S/C requires in particular precise attitude and position determination to minimize image quality degradation. The AOCS is based on the 3 axis strap-down attitude determination and zero momentum attitude control. The AOCS hardware and software are integrated to constitute the closed loop system (Figure 2). The AOCS introduces the following new components: 1) precision Star Tracker, 2) precision GPS Receiver capable of dual-frequency carrier phase measurement, and 3) a high-performance onboard computer, AOCE (Attitude & Orbit Control Electronics), based on new 64-bit spaceborne MPUs (Microprocessor Chips).
Attitude is sensed by the following devices: STT (Star Tracker) triplet configuration, IRU (Inertial Reference Unit), ESA (Earth Sensor Assembly), and carrier phase tracking of a GPS receiver (dual frequency). In addition, a laser corner-cube reflector is being used for SLR tracking services to calibrate the GPS receiver. The actuators used are: reaction wheels, magnetic torque rods and 16 hydrazine thrusters of RCS (Reaction Control Subsystem), each with a thrust of 1 N. A short-term attitude stability of ±0.00002º/0.37 ms (3σ) is provided; the long-term stability is ±0.0002º/5 s (3σ). The pointing accuracy knowledge is ±0.0002º, and the spacecraft position accuracy knowledge is ±1.0 m (a posteriori). The dual-frequency carrier-phase tracking GPS receiver of Toshiba Corp. is used for orbit determination. 5) 6) 7)
Figure 2: Block diagram of the AOCS closed-loop system (image credit: JAXA)
STT (Star Tracker). The ALOS STT is a key element in achieving required attitude determination accuracy. It is a precision fixed-head attitude sensor with a CCD detector design. STT has 3 optical heads (STO) and uses 2 optical heads simultaneously. It detects positions and the brightness of stars in its two fields of view (FOV), calculates corresponding addresses and intensity levels of the stars in its star tracker coordinate frame, and provides the results to the AOCE. 8) 9) 10)
Table 1: STT characteristics/specifications
Table 2: Major specifications of the AOCS 11)
The precision GPSR (GPS Receiver) is a key component to the position determination requirements of ALOS. JAXA developed developed the dual-frequency spaceborne GPS receiver that provides carrier phase measurement. GPSR measures pseudoranges and carrier phases of both L1 and L2 signals. The pseudorange of the L1 signal is used for the onboard, stand-alone (i.e., non-differential) position solution. AOCE compiles the navigation solution of GPSR as the “Payload Correction Data,” and provides accurate position information via TT&C to other subsystems such as the mission sensors. In addition, GPSR generates the precise reference time pulse, and serves as the reference clock of the intra-satellite time management.
On the ground, JAXA developed for ALOS the PPDS (Precision Pointing and Geolocation Determination System) that provides the pointing determination with an accuracy of 2.0º x 10-4, the attitude determination with the accuracy of 1.4º x 10-4, and the geolocation determination with an accuracy of 3 ~ 7.5 m. The system was developed for the geometric correction of PRISM imagery and the in-flight evaluation of the ALOS pointing requirements.
Figure 3: The ground PPDS (Precision Pointing and geolocation Determination System), image credit: JAXA
Figure 4: Artist's conception of the ALOS spacecraft - view 1 (image credit: JAXA)
Figure 5: Artist's conception of the ALOS spacecraft - view 2 (image credit: JAXA)
Launch: The ALOS spacecraft was launched on January 24, 2006 by a Japanese H-IIA rocket from the Tanegashima Space Center, Japan.
Orbit: Sun-synchronous near-recursive circular orbit, altitude = 691.65 km, inclination = 98.16º, repeat cycle = 46 days (with a sub-cycle of 2 days for event monitoring), local time at descending node 10:30 AM (±15 min), period = 98.51 min, orbits/day = 14 27/46.
RF communication and data distribution:
The primary data transmission link is via DRTS (Data Relay and Test Satellite of Japan) in Ka-band for mission data at 240 Mbit/s, and S-band for TT&C data. In addition there is an X-band downlink for maximum data rates of 120 Mbit/s. This is considered a backup only for AVNIR-2 data. A further Ka-band downlink at 120 Mbit/s is considered via the Artemis relay satellite of ESA. - ALOS is equipped with a solid-state recorder with a capacity of 768 Gbit using 64 Mbit DRAM technology. The storage capacity is sufficient for a 50 minute recording of a 240 Mbit/s data stream. The data rate capabilities of the recorder are: 360 Mbit/s for recording and 240 Mbit/s for readout of playback data.
The observation data produced by ALOS amount to about 1 TByte/day. In view of this large amount of data, JAXA proposed the concept of ADN (ALOS Data Node) to the international EO community. The benefits of this concept are:
• To increase capacity for ALOS data processing and archiving
• To accelerate practical and scientific use of ALOS data
• To increase international cooperation including joint validation and joint science study activities
• To enhance service for potential users.
The ALOS global acquisition concept consists of the following nodes:
Table 3: Overview of ALOS data node partners 12)
Figure 6: ALOS block diagram with data flow (image credit: JAXA/EORC)
Status of mission:
• On July 17, 2015, ESA released the ALOS image of Figure 7, covering part of the New York Metropolitan Area, including the island of Manhattan at the center, the boroughs Brooklyn, Queens (on the right),the Bronx along the top-right, and a part of Staten Island (bottom left). The Verrazano Bridge, connecting the New York City boroughs of Staten Island and Brooklyn, can be seen at the Harbor entrance of the Verrazano Narrows. The bridge has a central span of 1,298 m and was the longest suspension bridge in the world at the time of its completion in 1964. The bridge establishes a critical link in the local and regional highway system, and also marks the gateway to New York Harbor. 13)
- The Island of Manhattan is flanked on the east side by the East River and on the west side by the Hudson River (both 'rivers' are actually tidal estuaries). New Jersey is located to the west of the Hudson River. The Central Park in Manhattan, with a size of 340 hectares, is a prominent feature in the satellite image. The George Washington Bridge over the Hudson River can be seen at the very top of the image. It crosses the river between Fort Lee in New Jersey and the Washington Heights neighborhood of Manhattan.
- With over 8 million inhabitants on a limited amount of land, New York City is one of the most densely populated cities in the world. The city has a long history of land reclamation, most notably on the southwestern tip of Manhattan. This area was once part of the Hudson River before rock excavated during major construction projects and sand dredged from the Harbor were used to create the area known as Battery Park today.
Figure 7: ALOS image of New York City, acquired on June 18, 2010 (image credit: JAXA, ESA)
• May 18, 2015: JAXA started the publishing of a free of charge elevation data set that can express undulations of terrain over the world with a resolution of 30 m horizontally (30 m mesh version). The data set has been compiled with images acquired by ALOS/Daichi (Advanced Land Observing Satellite). As a first step, JAXA will offer the areas in East Asia, including Japan, and the South East Asia regions, and will expand the areas to all over the world (within ±82º of N/S latitudes). 14)
Figure 8: PRISM world elevation data (30 m mesh version); the yellow square indicates the area for the first publication (image credit: JAXA) 15)
- Digital 3D Topographic Data: The data set is published based on the elevation data set (5 m mesh version) of the “World 3D Topographic Data”. Digital 3D topographic data is data that records three dimensional coordinates (horizontal position and height) of terrain. The data consists of two kinds of data namely an ortho rectified image to show a horizontal position and digital elevation data to indicate height. An ortho- rectified image is compiled by removing distortion caused by terrain from an image taken from the sky and space, then adding correct information on the image. - Selecting about 3 million less clouded image scenes from all data acquired by the PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping) stereo imager aboard the ALOS/Daichi mission, JAXA compiles the digital elevation models of digital 3D topographic data. Thus, the models express the fine details of the world’s first 5 m resolution and an accuracy of 5 m height of the terrain over the world.
- JAXA has been processing about 100 digital 3D maps per month as part of its engineering validation activities of Daichi so far. With the research and development for full automatic and mass processing map compilations conducted, JAXA obtained a perspective to process 150,000 maps per month. By applying these research and development results, JAXA started the 3D map processing in March 2014 — the complete global 3D map is expected to be available in March 2016. JAXA will commission the compiling work and service provision to NTT DATA Corporation. 16) 17) 18)
Note: The ALOS-1/Daichi mission was launched on January 24, 2006. The spacecraft suffered a power failure in late April 2011 and could not be recovered by the project. ALOS-1/Daichi produced 5 years of observational data. PRISM was one of the instruments carried on ALOS. PRISM was designed to generate worldwide topographic data with its optical stereoscopic observation. The project processed semi-automatically DSM (Digital Surface Model) data with the image archives in some limited areas. The height accuracy of the dataset was estimated at less than 5m (rms) from the evaluation with GCPs (Ground Control Points) or reference DSMs derived from the LiDAR (Light Detection and Ranging). 19) 20)
Figure 9: Sample digital 3D image of Mount Everest (image credit: NTT Data, RESTEC, JAXA)
Table 4: Description of the AW3D30 DSM dataset
- NTT DATA Corporation and RESTEC ( Remote Sensing Technology Center), both with HQs located in Tokyo, Japan, distribute the digital 3D topographic data, covering the land of the entire world which shows undulations of terrain over the world in 5m resolution using PRISM data acquired by ALOS/Daichi (Advanced Land Observing Satellite) of JAXA (Japan Aerospace Exploration Agency). 21) 22)
Figure 10: Sample 3D image of a portion of the Grand Canyon (image credit: NTT Data, RESTEC, JAXA)
• November 14, 2014: This satellite image of JAXA' s ALOS mission was captured over southeastern Algeria in the heart of the Sahara desert. The heat and lack of water render vast desert areas highly unwelcoming, making satellites the best way to observe and monitor these environments on a large scale. 23)
Figure 11: The ALOS spacecraft acquired this AVNIR-2 image of the Sahara desert in Algeria on January 28, 2011 (image credit: JAXA, ESA)
Legend to Figure 11: In this image, a large area of rock appearing purple stretches across the right side of the image, with fluvial erosion patterns testament to an earlier time when the area received more rainfall. Today, this area sees an average of about 10 mm of rainfall per year. Wind-shaped sand dunes are visible on the left. The area at the bottom appears to be flat, with tiny specks of vegetation.
ALOS was supported as a Third Party Mission, which means that ESA used its multimission ground systems to acquire, process, distribute and archive data from the satellite to its user community.
• The western Indian city of Mumbai (formerly Bombay, officially renamed in 1995) is pictured in Figure 12 from Japan’s ALOS satellite. The image was released on Oct. 24, 2014 in ESA's Earth from Space video program. Mumbai is the capital city of the Indian state of Maharashtra. 24)
Figure 12: Image of Mumbai, India, acquired by ALOS on 23 March 2011 (image credit: JAXA, ESA)
Legend to Figure 12: Mumbai sits at the mouth of the Ulhas River – seen in the upper right – which carries sediments into the harbor and out to the Arabian Sea. Numerous vessels are visible in the waters, some of them approaching the city’s naturally deepwater harbor. To the west of Mumbai and across the water is Navi Mumbai, one of the world’s largest planned townships, developed to decongest Mumbai.
Mumbai is the fifth largest metropolitan area in the world, with a population of over 20 million. It is located on a claw-like peninsula of Salcette Island (center), which was originally seven separate islands until the 19th century, land reclamation projects joined them together.
The docks of Mumbai harbor are located on the east side of the peninsula. The curve at the bottom of the peninsula is Back Bay, and we can see the sands of the Chowpatty Beach within the curve. The oval green space on the west side of the city is the Mahalaxmi hourseracing track. Near the top of the image, one can see the Sanjay Gandhi National Park, with lakes and vast green areas.
• ESA's Earth from Space video program, released the ALOS image of Figure 13 on Sept. 19, 2014, showing Helsinki on the shores of the Gulf of Finland. The gulf is the eastern arm of the Baltic sea, stretching all the way to St Petersburg in Russia. The waters are relatively shallow, with an average depth of about 38 m and maximum depth of about 100 m. During winter – usually in January – the waters freeze and stay frozen until about April. 25)
Satellites play an important role during this season for shipping, providing imagery that helps icebreaker boats navigate through these frozen waters. Situated on the tip of a peninsula and on more than 300 islands, Helsinki is sparsely populated compared to other European capitals and has many green areas. Running north to south through the center of the city is a 10 km long forested park that offers opportunities for outdoor sports and activities to Helsinki’s residents.
North of the city, one can see the runways of the Helsinki airport, while farther west, the large, dark green area of Nuuksio National Park is evident.
Figure 13: The AVNIR-2 instrument of ALOS captured this image of Finland’s capital and largest city, Helsinki (upper right), on the shores of the Gulf of Finland on June 28, 2009 (image credit: ESA's Earth from Space video program)
• Northern Somalia’s Cal Madow mountain range is pictured in Figure 14 of Japan’s ALOS satellite, released in ESA's Earth from Space video program on July 25, 2014. ALOS was a TPM (Third Party Mission) of ESA. 26)
In contrast to the sparsely-vegetated majority of the country – typical of its semi-arid to arid climate – the mountain range is densely forested. In this image, the vegetated areas appear much darker. The ecologically diverse region is home to a number of endemic plants species, as well as many rare animals. Unfortunately, the area lacks proper conservation and is threatened by deforestation and intensive livestock grazing.
The uplifted plateau to the south has the distinct pattern of water erosion from rivers and streams making their way towards the edges of the cliffs, before cascading down. There are numerous perennial and persistent waterfalls in this region. In some areas, one can see where water continues to flow north across the coastal plain towards the Gulf of Aden (not pictured).
Figure 14: JAXA's ALOS satellite acquired this image of northern Somalia’s Cal Madow mountain range on January 2, 2011 (image credit: JAXA, ESA)
At 5199 m, Mount Kenya is the second highest peak in Africa. This stratovolcano is one of many volcanoes in the east of the Great Rift Valley (about 175km North-East of Nairobi), an area where two tectonic plates are moving apart. The mountain has 11 small glaciers but, like all glaciers on the high mountains of tropical Africa, they are rapidly retreating. Less snow accumulates during the winter than melts in the summer, and there is little to no formation of new ice. According to some predictions, there will no longer be any ice on the mountain in the next three decades. Mt. Kenya is an important water tower in the country. It provides water for about 50% of the country’s population and produces 70% of Kenya’s hydroelectric power.
The area around Mount Kenya is a national park protecting the biodiversity and forming an attractive destination for tourists, making it a key economic resource for the region. The area is home to monkeys, antelopes, elephants and leopards. The Mount Kenya National Park (2800 km2) and its natural forest has been an UNESCO World Heritage Site since 1997.
North of the mountain peak one can see a brown patchwork of fields, and a distinct line where the protected area ends and agriculture begins. In fact, a small portion of the park’s borders have fences and other barriers to keep animals within the reserve and off the farmland. In the upper right, there are large patches of light green, which are probably areas of failed agricultural development that now belong to the protected area.
Past threats from commercial tree plantations and other habitat destruction have been alleviated through long-term efforts, including the government’s policy of not converting any more natural forest for plantation development. But some areas that had been cleared but never planted are now colonized by grasses, and are being maintained as open grazing lands, rather than being allowed to revert to natural forest.
Figure 15: Mount Kenya, acquired with the AVNIR-2 instrument of ALOS on February 25, 2011 (image credit: JAXA, ESA)
Legend to Figure 16: The 40 km diameter circular Richat Structure is one of the geological features that is easier to observe from space than from down on the ground, and has been a familiar landmark to astronauts since the earliest missions. - Once thought to be the result of a meteor impact, researchers now believe it was caused by a large dome of molten rock uplifting and, once at the surface, being shaped by wind and water into what we see today. Concentric bands of resistant quartzite rocks form ridges, with valleys of less-resistant rock between them.
The dark area on the left is part of the Adrar plateau of sedimentary rock standing some 200 m above the surrounding desert sands. A large area covered by sand dunes – called an erg – can be seen in the lower-right part of the image, and sand is encroaching into the structure’s southern side.
Figure 16: Richat structure in the Sahara Desert of Mauritania, acquired on Nov. 23, 2010 with the AVNIR-2 instrument on ALOS (image credit: JAXA, ESA)
Figure 17: The AVNIR-2 instrument of ALOS captured this image of Margarita Island, Venezuela, on 26 June 2010 (image credit: ESA, JAXA)
Legend to Figure 17: Situated in the southern Caribbean Sea about 20 km off of mainland Venezuela’s coast, the island comprises two peninsulas linked by a long, narrow strip of land – called an isthmus. The eastern part of the island is home to most of the island’s residents, while the Macanao peninsula to the west is dominated by a central mountain range.
Between the peninsulas and cut off from the open sea by the isthmus lies the La Restinga lagoon, a national park that appears as a dark green and blue area in this image. Recognized as a wetland of international importance by the Ramsar Convention, the area features picturesque mangroves and is an important feeding ground for birds such as herons and flamingos. The shallow waters are home to red snappers, sardines and swordfish – among other types of fish – and oysters grow on the mangrove roots.
• Feb. 24, 2014: JAXA will compile a global digital 3D map with the highest precision in the world using some 3 million data images acquired by the ALOS (Advanced Land Observing Satellite) "DAICHI". The digital 3D map to be compiled has the world's best precision of 5 m in spatial resolution with 5 m height accuracy that enables the project to express land terrain on a global scale. Hence, its strong character will prove useful in various areas including mapping, damage prediction of a natural disaster, water resource research, etc. 32)
Figure 18: Digital 3D map image example of Mt. Everest (image credit: JAXA)
JAXA has been compiling about 100 digital 3D maps per month as part of the engineering validation activities of the DAICHI project. Since the project conducted research and development for full automatic and mass processing map compilations, there is now a perspective to process 150,000 maps per month. By applying the research and development results, the project will start the 3D map compilation in March 2014 to complete the global 3D map in March 2016. JAXA will commission the compiling work and service provision to NTT DATA Corporation. 33) 34)
In order to popularize the utilization of the 3D map data, JAXA will also prepare global DEMs (Digital Elevation Model s) with lower spatial resolution (of about 30 m under the current plan) to publish it as soon as it is ready. Its use will be free of charge. The project expects that data from Japan will become the base map for all global digital 3D maps (Ref. 32).
Figure 19: ALOS image of the heart of the Atacama Desert in Chile acquired on May 30, 2010 (image credit: ESA, JAXA)
Legend to Figure 19: The water of the lakes is brackish – meaning that it’s saltier than freshwater, but not as much as seawater. This is due to the salinity in the soil. Chile’s largest salt flat – the Salar de Atacama – lies to the west (not pictured). Two partially snow-covered volcanoes can be seen above and below the lakes on the right, while plains stretch out to the west in a nearly vegetation-free environment.
The area pictured is part of the Atacama Desert, which runs along part of South America’s central west coast. It is considered one of the driest places on Earth, as moisture from the Amazon Basin is blocked by the Andes to the east, as well as from the Pacific Ocean by the Chilean Coastal Range to the west. Pacific Ocean currents and wind circulation also play a major role in the desert climate.
Because of the Atacama plateau’s high altitude, low cloud cover and lack of light pollution, it is one of the best places in the world to conduct astronomical observations; it is the home to two major observatories.
• December 2013: ALOS image of Flinders Ranges (Figure 20), South Australia, about 500 km north of Adelaide, released in ESA's Earth from Space video program on Dec. 13, 2013. The area pictured is between Flinders Ranges National Park to the south, Vulkathunha-Gammon Ranges National Park to the north and Lake Frome due east (none of which is pictured). 36)
Figure 20: Flinders Ranges, South Australia. JAXA's ALOS spacecraft captured this image on 3 January 2009 (image credit: ESA's Earth from Space video program)
Legend to Figure 20: The curving structures that dominate this image are part of a larger geosyncline – a subsiding linear trough in Earth’s crust – that includes the Flinders Ranges. The geosyncline consists of sedimentary rocks in a basin that were folded about 500 million years ago and have been eroded to the current landscape. In this image, the different colors show the different layers of rock. Some of the oldest fossilized animal life have been found in parts of the Flinders Ranges.
Running up the middle of this image is a long, narrow gorge – typical of the ranges. Along the right side of the image, the terrain is flat with a long, straight road running north–south. Numerous creeks appear like veins across the entire image. The Flinders Ranges is one of Australia’s most seismically active regions, with numerous small earthquakes recorded every year.
• September 2013: The Al Jawf oasis in southeastern Libya is pictured in this image from Japan’s ALOS satellite. The city can be seen in in the upper left corner, while large, irrigated agricultural plots appear like Braille across the image. The two parallel runways of the Kufra Airport can seen between the city and the plots. 37)
Figure 21: Oasis image of the AVNIR-2 (Advanced Visible and Near Infrared Radiometer-2) instrument of ALOS acquired on Jan. 24, 2011 (image credit: ESA, JAXA)
Legend of Figure 21: The agricultural plots reach up to a 1 km in diameter. Their circular shapes were created by a central-pivot irrigation system, where a long water pipe rotates around a well at the center of each plot. Since the area receives virtually no rainfall, fossil water is pumped from deep underground for irrigation.
With the Sahara Desert making up most of Libya, only 6% of its territory is suitable for agriculture. Although Libya has no permanent rivers or natural inland water bodies, it has various vast fossil aquifers – natural underground basins that hold enormous amounts of fresh water. - These aquifers are a legacy from around 10,000 years ago, when this territory was home to rivers and lakes that were regularly replenished with rains. Heavy amounts of rainfall seeped underground to saturate subsurface sandstone, penetrating as deep as 4 km.
• August 2013: The ALOS mission of JAXA is also a TPM (Third Party Mission) of ESA. An AVNIR-2 (Advanced Visible and Near Infrared Radiometer-2) image of Asia Minor (Turkey) is shown in Figure 22 from ESA's data archive. Over the central high plains, the entire Lake Tersakan on the left side is seen, with part of Lake Tuz in the upper right corner. Lake Tuz is Turkey’s second largest lake, as well as one of the largest saline lakes in the world. 38)
Figure 22: The optical image of the ALOS satellite was acquired with AVNIR-2 on Oct. 21, 2010 over Anatolia’s dry, central plateau on the Asian side of Turkey (image credit: ESA)
Legend to Figure 22: While some of the surrounding land of Lake Tersakan shows the patchwork of agriculture, other areas are prone to the seasonal flooding of salty water. During the summer months, however, the lakewater recedes to expose a thick layer of salt. The bright white surface of the lake during the dry summer months has been used by Earth-observing satellites to calibrate their sensors for the color white – much like one would adjust a camera’s white balance setting. The salt from Lake Tuz is also mined, providing over half of the salt consumed in Turkey. In addition to its economic importance, the lake provides an important breeding ground for the Greater Flamingo and the Greater White-fronted Goose.
• The ALOS (Daichi) spacecraft was retired on May 12, 2011. The JAXA recovery team had been trying to communicate with ALOS for about three weeks after it developed a power generation anomaly. Since the project didn't see any way in recovering the communication with the satellite, JAXA decided to complete operations with the spacecraft and ended the mission. However, JAXA continues to investigate the causes of the power generation anomaly based on the data acquired from the satellite. 39)
ALOS, launched on January 24, 2006, had been operated for over five years, which was its target life and well beyond its design life of three years, and it achieved many fruitful results related to Earth observations. - In particular, ALOS contributed greatly to emergency observations of disaster-stricken areas. And thanks to Daichi's active contribution to overseas rescue operations at the time of major disasters, Japan received in return about 5,000 scenes of imagery from overseas at the time of the Great East Japan Earthquake in March 2011 through the International Charter Space and Major Disasters and from Sentinel Asia (Ref. 39).
• On April 22, 2011, the ALOS project noticed that the satellite had shifted its operation mode to the low load mode (i.e. the mode to save power consumption to maintain the minimum function of the satellite). As a consequence, all the onboard observation devices were turned off due to the anomaly of power generation reduction. JAXA is investigating the cause of this problem while taking necessary measures. 40)
• The Lighthouse Atoll in the Belize Barrier Reef in the Caribbean is featured in this image (Figure 23) acquired by Japan’s ALOS satellite with its AVNIR-2 (Advanced Visible and Near-Infrared Radiometer - 2) instrument. The greater Belize Barrier Reef has been a UNESCO World Heritage Site since 1996, but in 2009 it was put on the List of World Heritage in Danger. The reef provides a significant habitat for threatened species, including marine turtles, manatees and the American marine crocodile. 41)
Figure 23: The Lighthouse Atoll in the Belize Barrier Reef is featured in this image acquired on 29 March 2011 by Japan’s ALOS satellite (image credit: JAXA, ESA)
Legend to Figure 23: In the upper-central part of the image, an underwater sinkhole known as the Great Blue Hole appears as a dark blue circle. Surrounded by the shallow waters of the coral reef, the Great Blue Hole measures over 300 m in diameter and about 123 m deep. Formed when the sea level was much lower, rain and chemical weathering eroded the exposed terrain. Water later filled the hole and covered the area when the sea level rose at the end of the ice age. - Also visible in the image are two coral islands – green with vegetation – called cayes. The larger to the west is Long Caye, and the smaller Half Moon Caye is to the east.
• On March 11, 2011 (UTC), a magnitude 9.0 huge earthquake occurred off the Pacific coast of Tohoku-Kanto district of Japan (38.32ºN, 142.37ºE, 32 km in depth) accompanied by a massive tsunami. The earthquake and tsunami caused severe damage in many cities, and more than 20 thousand people were killed and lost their homes. JAXA performed emergency observations since the occurrence of the earthquake, using the PALSAR assembly on the ALOS. Figure 24 illustrates differential interferometric SAR (DInSAR) processing to detect crustal deformation associated with the earthquake. 42)
Figure 24: Mosaicked PALSAR interferogram of the earthquake region (image credit: JAXA)
• The ALOS (Daichi) spacecraft and its payload are operating nominally in the spring of 2011 after completing > 5 years on orbit.
- ALOS is well conditioned and may provide its services for more than 7 years (design life of 3 years, goal of 5 years). 43)
- The PALSAR instrument maintains a very good stability and high accuracy.
- An ALOS follow-on L-band SAR satellite is under development, ALOS-2, a launch is planned in 2013.
• On Dec. 20, 2010, a magnitude 6.5 earthquake occurred in southeastern Iran (28.49º N, 59.12º E, 11.8 km in depth). JAXA performed an emergency observation on December 31 using the PALSAR (Phased Array type L-band Synthetic Aperture Radar) instrument. A DinSAR (Differential interferometric SAR) processing was conducted to detect crustal deformation associated with the earthquake. 44)
Figure 25: The Betsiboka estuary in northwest Madagascar is pictured in this image from Japan’s AVNIR-2 of the ALOS spacecraft (image credit: ESA, JAXA)
Legend to Figure 25: The image was caputerd on Sept. 17, 2010 with AVNIR-2. In the Betsiboka estuary, Madagascar's argest river flows into Bombetoka Bay, which then opens into the Mozambique Channel. The red colouring of the sandbars and islands between the 'jellyfish tentacles' comes from sediments washed from hills and into the streams and rivers during heavy rain. The seaport city of Mahajanga can be seen in the upper-left corner of the image. 45)
Figure 26: Italy’s Lake Garda and the city of Verona south of the Italian Alps are pictured in this image from Japan’s ALOS observation satellite (image credit: ESA)
Legend to Figure 26: The image of the Alpine region was observed by the AVNIR-2 instrument on October 21,2010. ALOS was a Third Party Mission of ESA utilizing its multi-mission ground systems of existing national and industrial facilities and expertise to acquire, process and distribute data from the satellite.
With an area of 370 sq km, Lake Garda is the largest lake in Italy and the third largest in the Alpine region. It was formed by glaciers flowing out of the Alps during the last Alpine ice age, which ended around 12 000 years ago. East of the lake is the Adige River, flowing south before curving east toward Verona and then to the Adriatic Sea. 46)
Note: The ALOS-2 follow-up L-SAR mission of JAXA will be launched in 2013 (approved by the Japanese government in late 2008).
• ALOS has been operated successfully on orbit, delivering a variety of high-resolution images in numerous quantities and contributing to disaster management support many times. As of August 2008, the total images observed accumulated to 48,500,000 scenes, and 235 post-disaster observations have been provided (Ref. 7).
• On May 30, 2008, JAXA carried out a communication experiment with the University of Alaska in sending observation data of ALOS (Daichi) to the NASA White Sands Test Facility via the TDRS (Tracking and Data Relay Satellite) system of NASA (TDRS-F10). This represents the world's first data transmission test of this kind.
• In the timeframe 2007, some precision orbit control mechanisms were implemented to meet the stringent requirements for SAR interferometry. The flight results demonstrated that the requirements were achieved, and equator crossing points had been regulated within ±0.5 km from reference ground paths and altitude variations over some geo-locations had been kept within ±0.5 km. 49) 50) 51)
• So far in the mission (as of mid-2007), the TT&C communication system has been working to expectations in both direct S-band link and intersatellite S-band link and has provided stable and frequent communications for command and monitoring.
• On April 9, 2007, the DRC (Data Relay Communication) antenna suffered a loss of its primary TWTA (Traveling Wave Tube Assembly) for Ka-band transmission (intersatellite link to DRTS), but a redundant TWTA onboard ALOS made up the loss.
• The MDHS (Mission Data Handling System) has supported its data handling functions (compression, encoding, recording, and transmission) at data rates of 1360 Mbit/s (PRISM: 960 Mbit/s + AVNIR-2: 160 Mbit/s + PALSAR: 240 Mbit/s) properly everyday. The system achieved the world's first 240 Mbit/s Ka-band inter-satellite data transmission and has continued to process the world's largest generated data rate of space-based observation.
• The Ka-band transmission via DRTS provides an excellent stable link to receive very high bit rate data (277.56 Msample/s) from ALOS.
• Coverage of Niigata-ken Chuetsu Offshore Earthquake. A huge earthquake occurred off Jyo-chuetsu, Niigata Prefecture (60 km south-west of the city of Niigata), at about a depth of 17 km at 10:13 hours on July 16, 2007 Japan Standard Time (JST). JAXA analyzed observation images of PALSAR acquired by ALOS on July 19, 2007 - confirming the pattern of diastrophism. 52)
Figure 27: Diastrophism in Chuetsu Region, Niigata (image credit: JAXA)
• As of March 19, 2007, ALOS had provided support for 66 disaster monitoring requests within the last 14 months - providing imagery to various international, overseas, and domestic organizations such as the International Disaster Charter (IDC) and Sentinel-Asia, a disaster management support system in the Asia-Pacific Region.
• In March, 2007, another LLM retreat occurred initiated by power monitoring due to an operational error, although the satellite power system was in a perfect health. In addition, the criteria for RSP control (sub-satellite point cross-track control) were changed to improve SAR interferometry. The calibration parameters for STT and the precision attitude determination system were updated; furthermore the paddle drive control law software was reprogrammed in AOCS to improve attitude stability.
• In December 2006, a large solar flare and geomagnetic storm occurred. This required the execution of two sky maneuvers for seven days in total. ALOS retreated automatically into the safe mode (LLM) initiated by attitude check due to a software bug in a ground system and two operational problems.
• The commissioning phase of ALOS was successfully completed in April/May 2006 when JAXA initiated a worldwide CAL/VAL campaign together with several international partners to assess the data quality from the three onboard sensors. 53) 54) 55) 56)
• The first months after launch (until May 15, 2006) were dedicated to the initial check-out of the spacecraft, confirming the capabilities of all bus and mission subsystems and the end-to-end capabilities of the integrated system. On February 14-17, 2006, first images were captured by PRISM, AVNIR-2, and PALSAR. On February 20, 2006, a first post-disaster emergency monitoring was performed for the Leyte Island landslide of the Philippine. 57)
• ALOS began its operational phase on Oct. 24, 2006 and started distributing routinely its observational data products in Nov. 2006.
Figure 28: Alternate view of the ALOS spacecraft (image credit: JAXA)
Sensor complement: (PRISM, AVNIR-2, PALSAR, RRA)
PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping):
The objective is to obtain high-resolution stereo data (pixel size of 2.5 m) for cartographic applications (extraction of highly accurate digital elevation models, etc.). The instrument is a “three-line imager” with three independent catoptric systems for nadir, forward and backward-looking to achieve along-track stereoscopy. Each of the three telescopes employs a three mirror type optics design (30 cm aperture diameter and 2 m focal length) and several CCD detectors for pushbroom scanning. Six or eight silicon CCDs (5000 pixels each) are physically aligned at each telescope's focal plane. Of the 40,000 pixels per telescope, 14,000 pixels are electronically selected and transferred to the ground station. Thus, a triplet image consists of three (fore, nadir aft-looking) 14,000 pixels/line. - The nadir-looking telescope provides a swath of 70 km width (28,000 readout pixels), each of the fore and aft-looking telescopes provides a swath of 35 km (14,000 pixels per band). The fore and aft telescopes are inclined by ±23.8º from nadir to realize a base to height/ratio of one at an orbital altitude of 692 km. 58)
The PRISM optics are mounted on a rigid optical bench which is thermally controlled within ±3º C to minimize distortions in the optics system.
Table 5: PRISM parameters
Calibration: PRISM has electrical calibration sources onboard. They are used to estimate gain and offset of the amplifiers. For absolute and relative radiometric calibration, PRISM uses AVNIR-2 data. AVNIR-2 is calibrated using internal calibration lamps. During the commissioning phase, an extensive calibration and product validation campaign is being conducted. Highly accurate ground control points (GCP) are necessary to calibrate the geometric accuracy and to validate the generated DEMs (Digital Elevation Models). 59) 60)
Note: PRISM is now a separate sensor with stereo capability what used to be initially the “panchromatic sensor portion” of AVNIR-2.
Figure 29: Illustration of the PRISM instrument and three-line imaging configuration (image credit: JAXA)
Figure 30: Artist's view of PRISM imaging concept (image credit: JAXA)
AVNIR-2 (Advanced Visible and Near-Infrared Radiometer - 2):
AVNIR-2 is a JAXA instrument of AVNIR heritage flown on ADEOS, built by Mitsubishi Electric Corporation. Objective: provision of high-resolution (10 m) multispectral data. The instrument optics are of “folding Schmidt” type. The telescope aperture is 24 cm in diameter, it has a focal length of about 800 mm. AVNIR-2 features a pointing capability of ±44º in the across-track direction, thereby providing a wide field of regard (FOR) for disaster monitoring. The silicon CCD detector arrays have 7000 pixels per line (pushbroom type instrument). Applications: monitoring of regional environment (land coverage and land-use maps, etc.). A quasi-lossless data compression technique of DPCM (Differential Pulse Code Modulation) with Huffman coding is employed for a source data reduction from 160 Mbit/s to 120 Mbit/s. 61)
Calibration: AVNIR-2 uses two onboard calibration lamps which are used for absolute and relative calibration sequences. In addition, internal electrical calibration is provided.
Table 6: Some characteristics of the AVNIR-2 instrument
Figure 31: Illustration of AVNIR-2 observation capabilities (image credit: JAXA)
Figure 32: AVNIR-2 image of the Gulf of Naples, Italy, acquired on 28 April 2006 (image credit: ESA)
PALSAR (Phased Array L-band Synthetic Aperture Radar):
PALSAR was jointly developed by JAXA, JAROS (Japan Resources Observation System Organization) and METI (Ministry of Economy, Trade & Industry), heritage of SAR on JERS-1. PALSAR is a side-looking phased array L-band instrument with a pointing capability from 8 to 60º of incidence angle. The SAR antenna is of size: 8.9 m (length) and 3.1 m in width. An array of 80 transmitting/receiving modules (T/R) is mounted behind the antenna panels. Electrical beamsteering in elevation is provided. 62)
PALSAR features four operational modes:
• FB (Fine resolution Beam) mode: FB comprises 18 selections in the off-nadir angle range between 9.9º and 50.8º, each with 4 alternative polarizations: single polarization HH or VV, and dual polarization HH+HV or VV+VH. The bandwidth is 28 MHz in single polarization and 14 MHz in the dual-polarization modes. Out of the 72 possible FB modes, two have been selected for operational use.
• The 14 MHz polarimetric mode provides the full quad-polarization (HH+HV+VH+VV) scattering matrix with 12 alternative off-nadir angles between 9.7º and 26.2º.
• ScanSAR is available at a single polarization only (HH or VV) and can be operated with 3, 4, or 5 sub-beams transmitted in short (14 MHz) or long bursts (28 MHz). Out of the 12 ScanSAR modes available, the sort-burst, HH polarization, 5-beam mode has been selected for operational support. It features a 350 km swath width with an incidence angle range of 18-43º.
• The direct transmission (or downlink) mode is a contingency backup mode which allows the downlink of the (degraded, 14 MHz) FB mode data to local ground stations in case the high-speed DRTS (Data Relay and Test Satellite) becomes unavailable.
Polarization is changed in every pulse of transmission signal, and dual polarization signals are simultaneously received. The operation is limited in lower incident angle in order to achieve higher performances. At the nominal off-nadir angle (21.5º), the swath width is 30 km with 30 m spatial resolution under the maximum data rate condition (240 Mbit/s). 63)
Table 7: PALSAR default modes
Table 8: Observation parameter modes of the PALSAR instrument
Table 9: Some instrument characteristics of PALSAR
The high PALSAR data rates of 240 Mbit/s, generated in Fine, ScanSAR, and Polarimetric modes, will be transmitted mainly via DRTS (Data Relay Test Satellite) of JAXA. The modes of Direct downlink and ScanSAR (120 Mbit/s) can be received directly by the JAXA ground segment. The observation time of PALSAR will be in the order of 70 min/orbit (or about 70% duty cycle). 64) 65)
The NE (Noise Equivalent) σo (sigma zero) in Direct downlink mode is 3dB, better than that in Fine mode because the bandwidth of the receiver is half. Signal to ambiguity ratio (S/A) is specified both in azimuth and in range individually as more than 16dB within 70 km swath / 21dB within 60km swath at an off-nadir angle of 34.3º in Fine mode, and more than 21dB at #4 scan (off-nadir angle 34.1º) in ScanSAR mode.
The ALOS instruments are capable to observe the surface of the entire world within the following limits:
• Any place within two days
• Around the equator: about 60% of the area within one day
• At latitudes of 35º: about 70% of the area within one day
• At latitudes larger than 55º: any place every day (provided there is no cloud cover for the optical instruments).
Daytime observation modes: PRISM (fore, nadir & aft) and AVNIR-2 simultaneously
Nighttime observation modes: PALSAR (Note: AVNIR-2 and PALSAR are able to operate simultaneously).
Figure 33: Illustration of PALSAR observation capabilities (image credit: JAXA)
RRA (RetroReflector Array):
The objective is to provide support for precise orbit determination. The corner cubes are made of the highest quality fused silica. Their performance is optimized at the green wavelength (532 nm). The corner cubes are symmetrically mounted on a hemispherical surface with one nadir-looking corner cube in the center, surrounded by an angled ring of eight corner cubes. This will allow laser ranging in the field of view angles of 360º in azimuth and 60º elevation around the perpendicular to the satellite's -Zs Earth panel.
Figure 34: Illustration of the RRA (image credit: JAXA)
ALOS ground data system:
The ALOS ground data system function is allocated at JAXA/EOC (Earth Observation Center) for the provision of mission operation planning, data reception and recording, processing, archiving, and the distribution of ALOS data products. 70) 71) 72)
Figure 35: Overview of the ALOS ground data system (image credit: JAXA)
ALOS data distribution policy:
The significance of ALOS is its ability to provide global coverage of land observation and to transmit this huge amount of data acquired. JAXA seeks to implement the ADN (ALOS Data Node) concept for processing and utilizing ALOS data through international cooperation. The ALOS Data Node consists of one representative organization in each region and cooperative organizations including the data distributors. All the ALOS data is downlinked to JAXA's Earth Observation Center (EOC) via a data relay satellite or directly. JAXA will transfer the regional level-0 data it has obtained to the ALOS Data Node. The ALOS Data Node is responsible for providing regional level-1 data upon request from data users, including JAXA, throughout the ALOS mission life.
The current plan is to divide the entire world into four regions: Asia, Europe and Africa, North and South America, and Australia and Oceania. The Data Nodes will serve both as a regional ALOS data center and a scientific research center. Example Data Nodes are: 73) 74) 75)
• JAXA appointed RESTEC (Remote Sensing Technology Center) of Tokyo as the Primary Distributor (PD). RESTEC serves as the regional distributor in the Asia and Russian area as well as the coordinating agency among all of the regional distributors. The PALSAR products are produced at ERSDAC (Earth Remote Sensing Data Analysis Center), Japan.
• AADN (Americas ALOS Data Node) is provided by NOAA and ASF (Alaska Satellite Facility) at the Geophysical Institute, University of Alaska, Fairbanks. ASF and its partners will provide Level 0, Level 1 and higher order products to commercial and research users throughout North, Central and South America.
• ADEN (ALOS Data European Node) is provided by ESA (located at Esrange, Kiruna, Sweden). ESA is supporting ALOS as a 'Third Party Mission', which means the Agency utilizes its multi-mission ground systems of existing national and industrial facilities and expertise to acquire, process and distribute data from the satellite. 76) 77)
• NASA's TDRSS (Tracking and Data Relay Satellite System) started the downloading of ALOS (Daichi) SAR imagery in April 2010 - based on a collaboration agreement between JAXA and NASA in June 2009 (and one signed on April 13, 2010). The aim is to dramatically increase the frequency of observations for earthquake hazards, the decline of forests and changing water resources in North and South America.
The mutual agreement is part of the JAXA-NASA partnership in the field of satellites. The collaborative relationship includes JAXA's onboard devices on NASA's Aqua satellite and TRMM (Tropical Rainfall Measuring Mission), both of which are currently in operation, and NASA's onboard equipment on JAXA's Advanced Earth Observing satellites (ADEOS and ADEOS-II) in the past. In addition, NASA and JAXA plan to launch NASA's GPM (Global Precipitation Mission) on a JAXA launcher in 2013. 78) 79)
NASA's EDOS (Earth Observing System Data Operations System) multimission high-rate system provided operational support of ALOS data starting in April, 2010, and provided continuous operations until April, 2011 when the ALOS mission ended. EDOS successfully captured approximately 1,460 ALOS passes and processed approximately 36.5 TB of data during the one-year operational period. 80)
The main concept of the ALOS data policy should be that each Data Node would be allowed to handle their regional data according to its own data policy. International talks on this concept are about to produce an agreed inter-Node distribution policy defining an interface where the respective regional policies will meet. The whole mechanism will be a combination of de-centralized research and non-research data distribution. A private consortium may be established for promoting commercial data use.
At a multilateral level, nations have not been able to reach a coherent, effectively functioning data policy despite decades of lengthy discussions. If this Data Node concept is successfully implemented, it may demonstrate an effective model of a program-oriented approach to an integrated, disseminated data policy.
The ALOS Kyoto & Carbon Initiative is an international endeavour initialized by JAXA (former NASDA), with the main objective to support information needs raised by the UNFCCC (United Nations Framework Convention on Climate Change) Kyoto Protocol and by the international global carbon cycle science community, by provision of systematic, consistent, repetitive and regional scale data of the global forest cover. Of central importance for the Initiative is a Dedicated Data Acquisition Strategy for the polarimetric PALSAR instrument sensor onboard ALOS. 81)
PALSAR data distribution: Since JAXA and METI/JAROS (Ministry of Economy, Trade and Industry/Japan Resources Observation System Organization) jointly developed the PALSAR instrument, METI has an equal right to distribute the PALSAR data. Hence, ERSDAC (Earth Remote Sensing Data Analysis Center) of Tokyo, under METI agreement, will also distribute the PALSAR data. However, the ERSDAC initiative is outside of the ADN concept.
ALOS Kyoto and Carbon Initiative
JAXA has been working on the establishment of the ”ALOS Kyoto and Carbon Initiative” since 2003. The Initiative, led by JAXA/EORC, is being carried out as cooperative research with 20 international research institutions. The agreements were finalized on Aug. 23, 2007. The project started on Sept. 3, 2007. 82) 83)
The purpose of this project is to study the relationship between changes in the global environment and changes in forests, their surrounding areas, swamplands and deserts, which account for about 30% of the global land area, by observing their long-term and seasonal changes in a broad scope through the onboard synthetic aperture radar of the ALOS. (PALSAR). The study is based on the analysis of the observation data as well as a site survey. For this purpose, JAXA will carry out global observations including on tropical rain forests in South America (Amazon) Southeast Asia, and Central Africa, and the boreal forests in Siberia, Canada, and Alaska. Acquired data will be transmitted to each institution via exclusive online networks within three months after it is received at the Earth Observation Center (Hatoyama-machi, Saitama) of JAXA. In the case of data from the Amazon area, it is converted to images immediately, and provided to IBAMA (Brazilian Institute of Environment and Renewable Resources) within 10 days.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).