Ye, Nan
[Department of Civil Engineering, Monash University, Clayton, Australia]
Walker, Jeffrey P.
[Department of Civil Engineering, Monash University, Clayton, Australia]
Wu, Xiaoling
[Department of Civil Engineering, Monash University, Clayton, Australia]
de Jeu, Richard
[Transmittivity B.V., Space Technology Center, Noordwijk, The Netherlands]
Gao, Ying
[Department of Civil Engineering, Monash University, Clayton, Australia]
Jackson, Thomas J.
[USDA-ARS, Hydrology and Remote Sensing Laboratory, Beltsville, USA]
Jonard, François
[UCL]
Kim, Edward
[NASA Goddard Space Flight Center, Greenbelt, USA]
Merlin, Olivier
[CESBIO, Université de Toulouse, France]
Pauwels, Valentijn R. N.
[Department of Civil Engineering, Monash University, Clayton, Australia]
Renzullo, Luigi J.
[Fenner School of Environment and Society, The Australian National University, Canberra, Australia]
Rudiger, Christoph
[Department of Civil Engineering, Monash University, Clayton, Australia]
Sabaghy, Sabah
[Department of Civil Engineering, Monash University, Clayton, Australia]
von Hebel, Christian
[IBG-3, Forschungszentrum of Juelich, Germany]
Yueh, Simon H.
[NASA Jet Propulsion Laboratory, Pasadena, USA]
Zhu, Liujun
[Department of Civil Engineering, Monash University, Clayton, Australia]
The fourth and fifth Soil Moisture Active Passive Experiments (SMAPEx-4 and -5) were conducted at the beginning of the SMAP operational phase, May and September 2015, to: 1) evaluate the SMAP microwave observations and derived soil moisture (SM) products and 2) intercompare with the Soil Moisture and Ocean Salinity (SMOS) and Aquarius missions over the Murrumbidgee River Catchment in the southeast of Australia. Airborne radar and radiometer observations at the same microwave frequencies as SMAP were collected over SMAP footprints/grids concurrent with its overpass. In addition, intensive ground sampling of SM, vegetation water content, and surface roughness was carried out, primarily for validation of airborne SM retrieval over six ~ 3km × 3 km focus areas. In this study, the SMAPEx-4 and -5 data sets were used as independent reference for extensively evaluating the brightness temperature and SM products of SMAP, and intercompared with SMOS and Aquarius under a wide range of SM and vegetation conditions. Importantly, this is the only extensive airborne field campaign that collected data while the SMAP radar was still operational. The SMAP radar, radiometer, and derived SM showed a high agreement with the SMAPEx-4 and -5 data set, with a root-mean-squared error (RMSE) of ~ 3K for radiometer brightness temperature, and an RMSE of ~ 0.05 m3/m3 for the radiometer-only SM product. The SMAP radar backscatter had an RMSE of 3.4 dB, while the retrieved SM had an RMSE of 0.11 m3 /m3 when compared with the SMAPEx-4 data set.
Ye, Nan ; Walker, Jeffrey P. ; Wu, Xiaoling ; de Jeu, Richard ; Gao, Ying ; et. al. The Soil Moisture Active Passive Experiments: Validation of the SMAP Products in Australia. In: IEEE Transactions on Geoscience and Remote Sensing, Vol. 59, no.4, p. 2922-2939 (2021)