The nisar mission will provide global data sets of earth land surface dynamics that are critical to multiple earth science disciplines including observations of ecosystem carbon and water cycles. Soil…

The National Aeronautics and Space Administration (NASA) awarded a $342,895 grant to The Ohio State University to prepare for the production of a soil moisture product from the NISAR (NASA-ISRO Synthetic Aperture Radar) mission. NISAR will provide global data on land surface dynamics critical to monitoring ecosystem carbon and water cycles. The project will develop algorithms to estimate soil moisture and crop biomass using NISAR's L-band radar measurements, and support NISAR mission development activities. The Ohio State University has significant expertise in satellite remote sensing of soil moisture through participation in other missions like SMAP (Soil Moisture Active Passive). This grant does not have a set-aside designation.

The nisar mission will provide global data sets of earth land surface dynamics that are critical to multiple earth science disciplines including observations of ecosystem carbon and water cycles. Soil moisture is a surface hydrosphere state variable and plays a key role in global terrestrial hydrology. IT controls the partitioning of water and energy fluxes at the land surface. This partitioning affects not only the relative distribution between infiltration and surface runoff during precipitation, but also the energy exchange between the land and atmosphere systems. Vegetation water content in agricultural areas is a critical variable for food security and estimating crop yield. Nisar's l-band SAR backscatter measurements are similar to those planned for the l-band radar of the soil moisture active/passive (smap) mission, although at much finer spatial resolution. Despite the relatively short dataset available from the smap radar, analyses of this data set have shown the clear potential of a time series soil moisture retrieval algorithm to provide useful measurements of soil moisture. L-band radar observations have also shown the potential to estimate crop biomass. The proposed project will prepare for the production of a nisar soil moisture product through the use of a time series "ratio" algorithm previously demonstrated for the smap radar. The algorithm is based on the use of ratios of successive CO-POL SAR nrcs measurements, and is therefore insensitive to the nuisance parameters of surface roughness and vegetation attenuation for surface classes for which vegetation serves primarily as an attenuating effect. The method has also been extended to include the use of crosspol measurements to compensate for vegetation volume scattering prior to the application of the method. The proposed project will also develop algorithms for estimating crop biomass in agricultural areas. Cross-POL radar observations have shown to be sensitive to vegetation water content. The biomass estimates are critical for food security and crop yield. These estimates will be provided to USDA nass for yield estimates. The proposed project will develop the required algorithms for nisar measurements, will develop an error budget through simulation studies at multiple product spatial resolutions as well as any related recommendations for nisar operations to the nisar science team, and will develop a calibration/validation plan for post-launch activities leveraging past experience with smap CAL/VAL. The proposed project will also support participation in other mission development activities of the nisar science team with regard to land surface modeling and assessment of other radar effects on land surface products. The team is uniquely qualified and has developed and validated soil moisture products from multiple satellite missions (smap, aquarius, smos, AMSR2). Team members are part of the smap soil moisture algorithm development team and members of the cygnss, smap, aquarius and AMSR2 science teams.