Albedo
Measurement Types
Albedo describes how much sunlight a surface reflects rather than absorbs, and it is a key parameter for understanding the optical and energy properties of Earth’s surface. From deserts and forests to snowfields and oceans, every surface reflects light differently. Measuring albedo helps model energy exchange, improve land-surface and atmospheric correction algorithms, and track environmental change over time.
Albedo is defined as the proportion of incoming solar radiation reflected by a surface. Measuring this parameter requires observations of incoming and reflected solar radiation, making satellite-based Earth observations extremely valuable for collecting global albedo data. It is measured by comparing incoming solar radiation with outgoing reflected radiation across broad spectral ranges. 2) 3) 5) 7)
Ocean surfaces have a much lower albedo (around 0.1), while ice and snow have a higher albedo (around 0.85). Hence, surfaces covered in ice and snow, such as those found at the Earth’s poles, will reflect much more of the sun’s energy than the ocean. As the climate warms and the polar ice caps become smaller, more of the Earth’s surface is covered by ocean, increasing the amount of energy absorbed and warming the planet further. Sciences, such as those involved with the Global Tipping Points community, are actively studying these effects. 1) 4) 6)
The Earth’s radiation budget, a key study area of ESA and JAXA’s EarthCARE mission, is the balance between the energy the Earth receives from the Sun and the energy it emits back to space. It is linked very closely to albedo, and measurements of Earth’s albedo support studies of the radiation budget.
Example Products
A range of satellite missions provide global and regional albedo datasets supporting research, operational forecasting, and environmental monitoring. These products differ in spatial, spectral, and temporal coverage, but all contribute to a more complete understanding of how the Earth’s surface interacts with sunlight.
The following example products illustrate some of the available surface albedo products derived from satellite observations.
ESA Globalbedo
ESA’s Globalbedo product is a global broadband albedo map, covering the entire Earth’s land surface. The program produced a 15-year global albedo time series, ending in 2011 using ATSR-2, SPOT-4, and SPOT-5 observations. Globalbedo also validates and compares albedo product data against ground-based, airborne and other satellite measurements. 8)
VIIRS Land Surface Albedo
The Visible Infrared Imaging Radiometer Suite (VIIRS), carried by the Suomi National Polar Orbiting Partnership (Suomi NPP) mission, is used by NOAA to produce a land surface albedo product. VIIRS surface albedo is retrieved using a direct estimation method, where surface broadband albedo and VIIRS top of atmosphere reflectance are linked through statistical modelling. The direct retrieval algorithm generates primary surface albedo from VIIRS clear-sky observations, while data gaps in the clear-sky albedo granule are filled with historical albedo information, using a temporal filtering algorithm. The filled-gap albedo granule is known as Improved Surface Albedo. 9)
ECMWF Surface Albedo
The European Centre for Medium Range Weather Forecasts (ECMWF) Surface Albedo product is a 10-day gridded dataset, dating from 1981 to the present. This product first normalises reflectances, through inversion of a kernel-driven reflectance model, then computes directional albedo per spectral band through integration over the viewing hemisphere. Broadband albedo can then be calculated from the spectral albedo using a linear relationship. The ECMWF albedo product uses data from SPOT-4, Proba-V, and the Advanced Very High Resolution Radiometer (AVHRR), carried by MetOp-B and -C. 10)
Related Missions
A number of missions provide the multispectral, hyperspectral, and radar data used to derive or validate albedo products. The missions listed below illustrate the range of sensors contributing to global albedo records, from long-term optical imagers such as Landsat and MODIS to modern constellations such as Sentinel-2 and the RADARSAT series.
Landsat 7, 8 and 9
The Enhanced Thematic Mapper Plus (ETM+) instrument carried by Landsat 7 is a whiskbroom scanning radiometer that images in eight bands: four visible and near-infrared (VNIR), two shortwave infrared (SWIR), one thermal infrared (TIR), and one panchromatic (PAN) band. This multispectral imager allows Landsat 7 to capture reflectance data in each of these four spectral ranges.
Landsat 8, launched in February 2013, aims to collect thermal and multispectral imagery and ensure data continuity with previous Landsat missions. Landsat 9 was launched in September 2021, with the same mission objectives as Landsat 8. Landsat 8 carries the operational land imager (OLI), a moderate resolution multispectral imager. An identical instrument, OLI-2 is carried by Landsat 9 for data continuity. OLI and OLI-2 measure in spectral bands across Visible, VNIR and SWIR, allowing for the capturing of reflectance data to derive surface albedo.
Read more: Landsat 7, Landsat 8, Landsat 9
Sentinel-2
The Sentinel-2 constellation carries the multispectral instrument (MSI), which acquires imagery in 13 spectral bands: four visible, five near-infrared (NIR), two shortwave infrared (SWIR), and one band each for water vapour detection and cirrus detection. As a multispectral imager, MSI can be used to derive surface albedo, and its water vapour and cirrus detection capabilities enable atmospheric corrections.
MODIS
The Moderate-Resolution Imaging Spectrometer (MODIS) is a NASA instrument carried by the Terra and Aqua satellite missions. MODIS is an optomechanical imaging spectroradiometer, providing imagery in 36 spectral bands. This broad spectral coverage allows derivation of albedo and reflectance products from MODIS observations, such as snow and ice cover indices and vegetation and land surface products, both of which are reflectance derivatives.
AVHRR
The Advanced Very High Resolution Radiometer is a six-channel radiometer covering the visible, near infrared, shortwave infrared, mid-wave infrared and thermal infrared regions. The third generation of AVHRR instruments are carried by MetOp-B and -C, part of the joint ESA/EUMETSAT Meteorological Operational Satellite Program of Europe (MetOp), and was carried by the NOAA POES Series. AVHRR provides ice snow and vegetation cover measurements, using derived albedo and reflectance products from its captured spectral observations.
Joint Polar Satellite System
The Joint Polar Satellite System (JPSS) consists of four satellites, with JPSS-1 (NOAA-20) and JPSS-2 (NOAA-21) launched in November 2017 and 2022, respectively. All satellites carry the Visible Infrared Imaging Radiometer Suite (VIIRS), a multispectral opto-mechanical sensor that images in 22 bands. VIIRS data can be used to produce reflectance products, due to its broad spectral coverage.
Sentinel-5
Sentinel-5 is composed of the Ultraviolet/Visible/Near-Infrared/SWIR (UVNS) instrument aboard the Meteorological Operational Satellite - Second Generation A (MetOp-SG A) missions. UVNS is a pushbroom, passive spectrometer that covers a broad spectral range, allowing it to capture reflectance data. The mission provides operational monitoring of trace gas concentrations, meaning its data is also applicable in atmospheric corrections for surface reflectance products.
RADARSAT Constellation Mission
The RADARSAT Constellation Mission (RCM) is a constellation of three satellites, developed and operated by the Canadian Space Agency (CSA). While the C-band Synthetic Aperture Radar (SAR) observations obtained by the satellites cannot directly measure albedo, the surface characteristic data, such as confirming the presence of snow, ice, vegetation and topographical features, can be used to estimate albedo, or for validation and correction of reflectance and albedo models.
ALOS-2 & -4
The Advanced Land Observing Satellite (ALOS) missions 2 and 4 both carry versions of the Phased Array L-band SAR (PALSAR) instruments. Both PALSAR instruments use an active phased antenna array model, allowing both conventional stripmap and scanning imaging, as well as spotlight observations. These instruments provide land classification observations that are used for validation and correction of existing albedo and reflectance estimation models.
GCOM-C
The Global Change Observation Mission for Climate (GCOM-C) is a Japan Aerospace Exploration Agency (JAXA) mission that carries the Second Generation Global Imager (SGLI). SGLI is an advanced multipurpose imager that captures very near infrared, shortwave infrared and thermal infrared bands. The spectral coverage of the instrument allows it to be used in albedo and reflectance derivation, as thermal bands are commonly used in albedo estimation algorithms.
References
1) NASA EarthData, “Albedo”, URL: https://www.earthdata.nasa.gov/topics/land-surface/albedo
2) My NASA Data, “What is Albedo?”, URL: https://mynasadata.larc.nasa.gov/mini-lessonactivity/what-albedo
3) University Corporation for Atmospheric Research, “Albedo and Climate”, https://scied.ucar.edu/learning-zone/how-climate-works/albedo-and-climate
4) NASA EarthData, “Reflectance”, URL: https://www.earthdata.nasa.gov/topics/land-surface/reflectance
5) Nature Research Intelligence, “Land Surface Albedo and Reflectance Measurements”, URL: https://www.nature.com/research-intelligence/nri-topic-summaries/land-surface-albedo-and-reflectance-measurements-micro-48397
6) Global Climate Observing System, “Albedo”, URL: https://gcos.wmo.int/site/global-climate-observing-system-gcos/essential-climate-variables/albedo
7) NOAA/NASA, “Data Products: Land Surface Albedo”, URL: https://www.goes-r.gov/products/LSA.html
8) ESA, “Data User Element: Globalbedo”, URL: https://due.esrin.esa.int/page_project115.php
9) NOAA, “VIIRS Land Surface Albedo”, URL: https://www.ospo.noaa.gov/products/land/lsa/
10) Wekeo Copernicus, “Surface Albedo 10-daily gridded data”, URL: https://wekeo.copernicus.eu/data?view=dataset&dataset=EO%3AECMWF%3ADAT%3ASATELLITE_ALBEDO