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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Hydrology and Remote Sensing Laboratory » Research » Publications at this Location » Publication #316288

Title: Inter-comparison of SMAP, Aquarius and SMOS L-band brightness temperature observations

Author
item Jackson, Thomas
item BINDLISH, R. - Collaborator
item PIEPMEIER, J. - National Aeronautics And Space Administration (NASA)
item YUEH, S. - Jet Propulsion Laboratory
item KERR, Y. - Collaborator

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2015
Publication Date: 7/26/2015
Citation: Jackson, T.J., Bindlish, R., Piepmeier, J. , Yueh, S., Kerr, Y. 2015. Inter-comparison of SMAP, Aquarius and SMOS L-band brightness temperature observations International Geoscience and Remote Sensing Symposium. July 26-31, 2015, Milan, Italy. 2015 CDROM

Interpretive Summary:

Technical Abstract: Soil Moisture Active Passive (SMAP) mission is scheduled for launch on January 29, 2015. SMAP will make observations with an L-band radar and radiometer using a shared 6 m rotating reflector antenna. SMAP is a fully polarimetric radiometer with the center frequency of 1.41 GHz. The target accuracy of the SMAP radiometer is 1.3 K. The SMAP radiometer will have a swath width of 1000 km and with an exact repeat orbit of 8 days. The spatial resolution will be 40 km and products will be posted to a fixed 36 km grid. Currently, Soil Moisture Ocean Salinity (SMOS) and Aquarius provide global L-band radiometer measurements. SMAP will be the third L-band radiometer concurrently operating in space. It will be beneficial to the end users of these data if the observations made at the same frequency,polarizations, and incidence angle by multiple instruments/platforms (at concurrent locations and times) are consistent with each other. If the brightness temperature (TB) observations from the SMAP, Aquarius and SMOS missions are made at the same time and location they should be similar. This provides both an opportunity to build a more robust data set of soil moisture and TB and to cross-calibrate and compare the L-band TB observations from different satellite missions. Consistent calibration across all satellite missions will be critical to eventually developing a long term climate data record of L-band TB observations. A physically-based soil moisture algorithm that spans multiple L-band missions requires consistent input observations for the development of a long term environmental data record. It is a challenge to validate TB over land (as opposed to oceans) using models because there are more factors that contribute to TB and the footprints are more heterogeneous. On the other hand, the inter-comparison of the two sensors provides a consistency check on the calibration. Inter-comparison of SMAP L-band brightness temperatures with SMOS and Aquarius can be used as a useful tool for radiometer Level 1 (L1) calibration. Microwave observations from the SMOS mission were reprocessed to approximate SMAP microwave radiometer observations that will be made at a constant incidence angle of 40 degrees. The SMOS data were also reprocessed to match the incidence angle and sizes of the three Aquarius radiometer footprints. The inter-comparison between the simulated SMAP and SMOS observations showed significant scatter for both H and V polarizations. The scatter is greater for H pol observations. H polarization observations are more sensitive to changes in land surface conditions (soil moisture and surface temperature). The land surface model generally has a higher soil moisture estimate resulting in lower brightness temperature simulations. The differences are greater for H polarization than V polarization. However, these are simulations and do not reflect real-world conditions. SMAP L1 “beta” products will be released 3 months after in-orbit check-out (July 2015). Analyses will be conducted using the SMAP “beta” release L1 product and the latest SMOS and Aquarius data available. SMAP observations will be compared directly with the Aquarius middle beam brightness temperature observations, after aggregating them to match the size of the Aquarius footprint. Intercomparison of SMAP L-band brightness temperatures with SMOS and Aquarius will provide a useful tool to access the SMAP radiometer L1 calibration.