SMAP-3

Abstract: Satellite sensor systems for soil moisture measurements have been continuously evolving.
The Soil Moisture Active Passive (SMAP) mission represents one of the latest advances in this regard.
Thus far, much of our knowledge of the accuracy of SMAP soil moisture over the Great Lakes region
of North America has originated from evaluation studies using in situ data from the U.S. Department
of Agriculture (USDA) Natural Resources Conservation Service Soil Climate Analysis Network
and/or the U.S. Climate Reference Network, which provide only several in situ sensor stations for
this region. As such, these results typically underrepresent the accuracy of SMAP soil moisture
in this region, which is characterized by a relatively large soil moisture variability and is one of
the least studied regions. In this work, SMAP Level 2-4 soil moisture products: SMAP/Sentinel-1
L2 Radiometer/Radar Soil Moisture (SPL2SMAP_S), SMAP Enhanced L3 Radiometer Soil Moisture
(SPL3SMP_E), and SMAP L4 Surface and Root-Zone Soil Moisture Analysis Update (SPL4SMAU)
are evaluated over the southern portion of the Great Lakes region using in situ measurements from
Michigan State University’s Enviro-weather Automated Weather Station Network. The unbiased
root-mean-square error (ubRMSE) values for both SPL4SMAU surface and root zone soil moisture
estimates are below 0.04 m3 m−3 at the 36-km scale, with an average ubRMSE of 0.045 m3 m−3
(0.037 m3 m−3
) for the surface (root-zone) soil moisture against the sparse network. The ubRMSE
values for SPL3SMP_E a.m. (i.e., descending overpasses) soil moisture retrievals are close to or below
0.04 m3 m−3 at the 36-km scale, with an average ubRMSE of ~0.06 m3 m−3 against the sparse network.
The average ubRMSE values are ~0.05-0.06 m3 m−3
for high-resolution SPL2SMAP_S soil moisture
retrievals against the sparse network, with the skill of the baseline algorithm-based soil moisture
retrievals exceeding thaThe PI-produced JPL V5.0 SMAP Sea Surface Salinity (SSS) and extreme winds Level 3 (L3) standard datasets is based on the JPL Combined Active-Passive (CAP) algorithm applied to data from the NASA Soil Moisture Active Passive (SMAP) observatory. For science applications, use of the standard products is strongly advised.

They also recommend the use of the V5.0 forward stream data over the prior version, which is deprecated and will be retired within the next 6 months. JPL SMAP V5.0 SSS is based on the newly released SMAP V5 Level-1 Brightness Temperatures (TB). An enhanced calibration methodology has been applied to the brightness temperatures, which improves absolute radiometric calibration and reduces the biases between ascending and descending passes. The improved SMAP TB Level 1 TB will enhance the use of SMAP Level-1 data for other applications, such as sea surface salinity and winds. Data begins on 1 April 2015 and is ongoing. Datasets comprising this release include the L2B orbital data and two L3 mapped, global coverage salinity datasets: an 8-day running mean dataset based on the repeat orbit of the SMAP mission, along with a monthly average dataset. The L3 data are gridded at 0.25 x 0.25. The spatial resolution of all four datasets is approximately 60 km.

The JPL SMAP-SSS CAP V5.0 datasets are described and discoverable via the PO.DAAC data portal.