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HARP (Hyper-Angular Rainbow Polarimeter)

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HARP is a NASA/ESTO (Earth Science Technology Office) funded CubeSat mission under the InVEST (In-Space Validation of Earth Science Technologies) Program. The HARP CubeSat mission is a joint effort between the UMBC (University of Maryland Baltimore County), Catonsville, MD, USU/SDL (Utah State University/Space Dynamics Laboratory ), North Logan, UT, STC (Science and Technology Corporation) with HQ in Hampton, VA, and NASA/GSFC (Goddard Space Flight Center) in Greenbelt, MD. The goal is to deploy the HARP CubeSat from the ISS. The desired mission life consists of three months for technology demonstration and an extended science data period of another seven months, which will total almost a year on orbit.

The HARP mission is designed to measure the microphysical properties of cloud water and ice particles in the atmosphere. HARP is a precursor for the new generation of imaging polarimeters to be used for the detailed measurements of aerosol and cloud properties. The HARP payload is a wide FOV (Field of View) imager that splits three spatially identical images into three independent polarizers and detector arrays. This technique achieves simultaneous imagery of three polarization states and is the key innovation to achieve high polarimetric accuracy with no moving parts.

The objectives of the HARP demonstration mission are: 1) 2)

• Validate the in-flight capabilities of a highly accurate and precise wide field of view hyper-angular polarimeter for characterizing aerosol and cloud properties.

• Prove that CubeSat technology can provide science-quality multi angle imaging data paving the way for lower cost aerosol-cloud instrument developments.

• Provide opportunities for student research and engineering training in implementing a space mission.

The HARP science goal is to demonstrate the ability to characterize the micro physical properties of aerosols and clouds at the scale of individual moderate-sized clouds for the ultimate purpose of narrowing uncertainties in climate change.

The PI (Principal Investigator) of the HARP mission is J. Vanderlei Martins of UMBC. The Co-Is/Partners are: Lorraine Remer, JCET-UMBC; Tim Nielsen, USU/SDL; Leroy Sparr, NASA/GSFC; Mark Schoeberl, STC. 3)

HARP is a potential precursor for the polarimeter in ACE (Aerosol-Clouds and Echosystems) and other future NASA missions.


The HARP CubeSat mission will be a joint effort between UMBC, the PI institution, who will provide the instrument and characterization and scientific analysis; the Space Dynamics Laboratory – Utah State University, who will provide the 3U CubeSat spacecraft and mission operations; and the Science and Technology Corporation, who will lead the science algorithm development and science application funded by NOAA. NASA Wallops will support instrument environmental testing, mission operations, and communications.

The 3U CubeSat is 3-axis stabilized designed to keep the imager pointing nadir during the data acquisition period. The hyper-angular capability is achieved by acquiring overlapping images at very fast speeds.


Figure 1: Illustration of the HARP nanosatellite (image credit: HARP Team)


Figure 2: HARP –full feature Earth sciences satellite (image credit: USU/SDL) 4)

Launch: The HARP nanosatellite was launched as a secondary payload on an ISS logistics mission of Orbital ATK (Cygnus OA-7 , also known as CRS-7)on April 18. The launch vehicle was Atlas-5 401 of ULA and the launch site was Cape Canaveral (SLC-41), FL. 5) 6)

Orbit: Near-circular orbit, altitude of ~ 400 km, inclination of 51.6º.

The ISS orbit has the advantage of allowing HARP to cross many other Earth Science Satellites (including Terra, Aqua, Aura, VIIRS on Suomi NPP, CALIPSO, etc.) and produce intercomparisons and a synergistic use of the HARP data together with data from these other platforms.

Secondary payloads (CubeSats): 7)

• Altair-1, a 6U CubeSat technology demonstration mission of Millennium Space Systems, El Segundo, CA, USA.

• IceCube, a NASA/GSFC 3U CubeSat technology demonstration mission.

• HARP (Hyper-Angular Rainbow Polarimeter), a 3U CubeSat of UMBC (University of Maryland, Baltimore County), USU/SDL and STC (Science and Technology Corporation).

• CSUNSat-1, a 2U CSUN (CubeSat of California State University Northridge), CA.

• CXBN-2 (Cosmic X-Ray Background-2), a 2U CubeSat of Morehead State University, Morehead, Kentucky.

• OPEN (Open Prototype for Educational NanoSats), a 1U CubeSat of UND (University of North Dakota).

• Violet, a 1U CubeSat of Cornell University, Ithaca, N.Y.

• Biarri-Point, a 3U CubeSat technology mission, a four nation defence related project involving Australia, the US, the UK and Canada. Biaari is an RF signal collection mission that can be related to the spot beam mapping mission through mutual use of GPS signals. 8) 9)

• QB50 x 28. Twentyeight CubeSats of the international QB50 constellation, a European FP7 Project for Facilitating Access to Space and managed by the Von Karman Institute for Fluid Dynamics in Brussels, were flown to the ISS for subsequent deployment. The 28 CubeSats of the QB50 constellation were integrated into 11 NanoRacks 6U deployers. 10)

In addition, four Lemur-2 satellites, operated by Spire Global Inc. of San Francisco , were launched aboard the Cygnus OA-7 cargo craft to replenish and expand the company’s constellation dedicated to obtaining global atmospheric measurements for operational meteorology and tracking ship traffic across the planet for various commercial applications. The four Lemur-2 CubeSats are mounted externally to the cargo ship. After Cygnus departs the station in July, it will climb to a higher altitude, around 500 km, and eject them into space.

Sensor complement: (Imaging Polarimeter)

HARP will be the first US imaging polarimeter in Space. Polarization measurements are used because the technique provides new information on aerosol and cloud properties and their interaction. HARP design is an advance over POLDER’s (POLarization and Directionality of the Earth's Reflectances) filter wheel system. The HARP polarimeter will provide full cloudbow retrievals from a small area (< 4 km x 4 km from space).

Cloud and aerosol processes influence climate change, which affect our oceans, weather, ecosystems, and society. The largest impediments to estimating climate change revolve around a lack of quantitative information about aerosol forcing, insufficient understanding of aerosol-cloud processes, and cloud feedbacks in the climate system. The climate community requires new observations and a better understanding of aerosol and cloud processes to narrow climate change estimate uncertainties. The aerosol community requires a multi-wavelength, multi-angle imaging polarimeter with the wide FOV imaging heritage of the POLDER mission and the high accuracy promised by the APS (Aerosol Polarimetry Sensor). Unfortunately, APS was lost when the Glory mission failed to reach orbit.

An imaging polarimeter with hyperangular capability can make a strong contribution to characterizing cloud properties, especially ice clouds. Because of their sensitivity to thin cirrus clouds, non-polarized multi-angle measurements can be used to provide climatology. Adding polarization and increasing the number of observation angles provides a much clearer picture of cloud droplet distribution, adding size and width measurements to the currently measured effective radius. The combination of hyperangular polarized measurements and short-wave infrared channels (2.1 µm) should also provide enough constraints to determine important characteristics of cloud ice crystals. In the coming decades, it will be important to have an imaging polarimeter with the capability to characterize both aerosols and clouds. Highly-capable, small, and versatile, HARP is designed to meet the needs of both the aerosol and cloud communities.

The HARP payload, a hyperangular imaging polarimeter that can see Earth from multiple viewing angles, 4 wavelengths, and three polarization angles was developed and is being built at LACO (Laboratory for Aerosol, Clouds and Optics) in the Physics Department at UMBC with support from JCET (Joint Center of Earth Systems and Technology) and NASA/GSFC (Goddard Space Flight Center). The HARP science algorithms will be developed in collaboration between UMBC and STC (Science and Technology Corporation). The main characteristics of the HARP payload are described in Table 1. 11) 12)

• One hyper-angular channel with up to 60 viewing angles per pixel at 670 nm (for cloudbow measurements)

• Three channels with up to 20 viewing angles per pixel at 440, 550, 670 nm

• Goal of one additional channel with up to 20 viewing angles at 870 nm

• 2.5 km nadir resolution (from 650 km orbit)

• 94 degree FOV in cross-track

• 110 degree FOV in along track

Table 1: Polarimeter specifications

HARP is designed to see how aerosols interact with the water droplets and ice particles that make up clouds. Aerosols and clouds are deeply connected in Earth's atmosphere – it's aerosol particles that seed cloud droplets and allow them to grow into clouds that eventually drop their precipitation (Figure 3). 13)

This interdependence implies that modifying the amount and type of particles in the atmosphere, via air pollution, will affect the type, size and lifetime of clouds, as well as when precipitation begins. These processes will affect Earth's global water cycle, energy balance and climate.

When sunlight interacts with aerosol particles or cloud droplets in the atmosphere, it scatters in different directions depending on the size, shape and composition of what it encountered. HARP will measure the scattered light that can be seen from space. We'll be able to make inferences about amounts of aerosols and sizes of droplets in the atmosphere, and compare clean clouds to polluted clouds.

In principle, the HARP instrument would have the ability to collect data daily, covering the whole globe; despite its mini size it would be gathering huge amounts of data for Earth observation. This type of capability is unprecedented in a tiny satellite and points to the future of cheaper, faster-to-deploy pathfinder precursors to bigger and more complex missions.

HARP is one of several programs currently underway that harness the advantages of CubeSats for science data collection. NASA, universities and other institutions are exploring new earth sciences technology, Earth's radiative cycle, Earth's microwave emission, ice clouds and many other science and engineering challenges.


Figure 3: Pollution particles lead to precipitation changes (image credit: Martins, UMBC, CC BY-ND)


Figure 4: Artist's illustration of HARP specialized to perform the delicate multi-angle, multi-spectral polarization measurements (image credit: HARP Team)


Figure 5: Photos of the spacecraft and the actual instrument (image credit: HARP Team)

The HARP polarimeter is fully programmable and will allow for the selection of different spatial resolutions and combinations of wavelengths and viewing angles depending on the science interest and total amount of data to downlink. The different along track viewing angles from HARP will allows the observations of targets on the ground from different viewing perspectives. These different viewing observations of the same target allow for additional information from the target facilitating the quantitative retrieval of information from the atmosphere and surface properties such as the aerosol particle amount, the cloud droplet sizes, and specific characteristics of Earth’s surface.


Figure 6: Photo of the stripe filter unit (image credit: HARP Team)


Figure 7: HARP calibration (image credit: HARP Team)


Figure 8: A series of pictures of the coast of California taken during the PODEX (Polarimeter Definition Experiment) campaign by the PACS multi-angle imaging polarimeter taken from the NASA ER-2 aircraft (image credit: NASA)

Legend to Figure 8: The PACS (Passive Aerosol & Clouds Suite) polarimeter serves as an airborne simulator for the HARP imaging polarimeter. The different perspectives in the images emphasize the variation of the reflection of the sun on the ocean surface as a function of the viewing angle. In some along track viewing angles this reflection disappears while in other angles this reflections appear very intensively.

UMBC SOC (University of Maryland Baltimore County - Science Operations Center)


Figure 9: UMBC SOC - HARP level 1B data production (image credit: HARP Team)


Figure 10: UMBC SOC - Level 2 algorithm (image credit: HARP Team)

1) J. Vanderlei Martins, ”HARP: Hyper-Angular Rainbow Polarimeter CubeSat,” ESTO Science and Technology Forum, June 14, 2016, URL:

2) ”HARP Hyper-Angular Rainbow Polarimeter,” USU/SDL, URL:

3) ”Hyper-Angular Rainbow Polarimeter (HARP) CubeSat,” Feb. 2015, URL:

4) J. Vanderlei Martins, Tim Nielsen, Chad Fish, Leroy Sparr, Roberto Fernandez-Borda, Mark Schoeberl, Lorraine Remer, ”HARP CubeSat–An innovative Hyperangular Imaging Polarimeter for Earth Science Applications,” Small Sat Pre-Conference Workshop, Logan Utah, 3 Aug 2014, URL:

5) ”NASA Space Station Cargo Launches aboard Orbital ATK Resupply Mission,” NASA, Release 17-029, April 18, 2017, URL:

6) Jeff Foust, ”Orbital to launch next Cygnus mission on Atlas 5,” Space News, Nov. 4, 2016, URL:

7) ”United States Commercial ELV Launch Manifest,” Dec. 28, 2016, URL:

8) Eamonn P. Glennon, Joseph P. Gauthier, Mazher Choudhury, Kevin Parkinson, Andrew G. Dempster, ”Project Biarri and the Namuru V3.2 Spaceborne GPS Receiver,” IGNSS (International Global Navigation Satellite Systems Society) Symposium 2013, Outrigger Gold Coast, Australia, 16 – 18 July 2013, URL:

9) Jacob A. LaSarge, ”A CubeSat mission for mapping spot beams of geostationary communication satellites,” Thesis, March 2015, URL:

10) Davide Masutti, ”QB50-ISS CubeSats ready to be launched,” Dec. 9, 2016, URL:

11) ”HARP Overview,” UMBC/LACO, URL:

12) Brent McBride, ”Polarimetric remote sensing with the Hyper-Angular Rainbow Polarimeter, 3U CubeSat,” Sept. 17, 2015, URL:

13) Vanderlei Martins, ”Tiny satellites poised to make big contributions to essential science,” UMBC, January 27, 2017, URL:

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 (

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