TY - JOUR
T1 - Version 4 of the SMAP Level-4 Soil Moisture Algorithm and Data Product
AU - Reichle, Rolf H.
AU - Liu, Qing
AU - Koster, Randal D.
AU - Crow, Wade T.
AU - De Lannoy, Gabrielle J.M.
AU - Kimball, John S.
AU - Ardizzone, Joseph V.
AU - Bosch, David
AU - Colliander, Andreas
AU - Cosh, Michael
AU - Kolassa, Jana
AU - Mahanama, Sarith P.
AU - Prueger, John
AU - Starks, Patrick
AU - Walker, Jeffrey P.
N1 - Publisher Copyright:
© 2019. The Authors.
PY - 2019/10/1
Y1 - 2019/10/1
N2 - The NASA Soil Moisture Active Passive (SMAP) mission Level-4 Soil Moisture (L.4_SM) product provides global, 3-hourly, 9-km resolution estimates of surface (0–5 cm) and root zone (0–100 cm) soil moisture with a mean latency of ~2.5 days. The underlying L4_SM algorithm assimilates SMAP radiometer brightness temperature (Tb) observations into the NASA Catchment land surface model using a spatially distributed ensemble Kalman filter. In Version 4 of the L4_SM modeling system the upward recharge of surface soil moisture from below under nonequilibrium conditions was reduced, resulting in less bias and improved dynamic range of L4_SM surface soil moisture compared to earlier versions. This change and additional technical modifications to the system reduce the mean and standard deviation of the observation-minus-forecast Tb residuals and overall soil moisture analysis increments while maintaining the skill of the L4_SM soil moisture estimates versus independent in situ measurements; the average, bias-adjusted root-mean-square error in Version 4 is 0.039 m3/m3 for surface and 0.026 m3/m3 for root zone soil moisture. Moreover, the coverage of assimilated SMAP observations in Version 4 is near global owing to the use of additional satellite Tb records for algorithm calibration. L4_SM soil moisture uncertainty estimates are biased low (by 0.01–0.02 m3/m3) against actual errors (computed versus in situ measurements). L4_SM runoff estimates, an additional product of the L4_SM algorithm, are biased low (by 35 mm/year) against streamflow measurements. Compared to Version 3, bias in Version 4 is reduced by 46% for surface soil moisture uncertainty estimates and by 33% for runoff estimates.
AB - The NASA Soil Moisture Active Passive (SMAP) mission Level-4 Soil Moisture (L.4_SM) product provides global, 3-hourly, 9-km resolution estimates of surface (0–5 cm) and root zone (0–100 cm) soil moisture with a mean latency of ~2.5 days. The underlying L4_SM algorithm assimilates SMAP radiometer brightness temperature (Tb) observations into the NASA Catchment land surface model using a spatially distributed ensemble Kalman filter. In Version 4 of the L4_SM modeling system the upward recharge of surface soil moisture from below under nonequilibrium conditions was reduced, resulting in less bias and improved dynamic range of L4_SM surface soil moisture compared to earlier versions. This change and additional technical modifications to the system reduce the mean and standard deviation of the observation-minus-forecast Tb residuals and overall soil moisture analysis increments while maintaining the skill of the L4_SM soil moisture estimates versus independent in situ measurements; the average, bias-adjusted root-mean-square error in Version 4 is 0.039 m3/m3 for surface and 0.026 m3/m3 for root zone soil moisture. Moreover, the coverage of assimilated SMAP observations in Version 4 is near global owing to the use of additional satellite Tb records for algorithm calibration. L4_SM soil moisture uncertainty estimates are biased low (by 0.01–0.02 m3/m3) against actual errors (computed versus in situ measurements). L4_SM runoff estimates, an additional product of the L4_SM algorithm, are biased low (by 35 mm/year) against streamflow measurements. Compared to Version 3, bias in Version 4 is reduced by 46% for surface soil moisture uncertainty estimates and by 33% for runoff estimates.
KW - Catchment land surface model
KW - L-band passive microwave
KW - Soil Moisture Active Passive
KW - data assimilation
KW - runoff
KW - soil moisture
UR - http://www.scopus.com/inward/record.url?scp=85074289293&partnerID=8YFLogxK
U2 - 10.1029/2019MS001729
DO - 10.1029/2019MS001729
M3 - Article
AN - SCOPUS:85074289293
SN - 1942-2466
VL - 11
SP - 3106
EP - 3130
JO - Journal of Advances in Modeling Earth Systems
JF - Journal of Advances in Modeling Earth Systems
IS - 10
ER -