Comparison of high-resolution airborne soil moisture retrievals to SMAP soil moisture during the SMAP validation experiment 2016 (SMAPVEX16)

REMOTE SENSING OF ENVIRONMENT

卷:227

Article

Colliander, Andreas¹  Cosh, Michael H.²  Misra, Sidharth¹  Jackson, Thomas J.²  Crow, Wade T.²  Powers, Jarrett³  McNairn, Heather³  Bullock, Paul⁴  Berg, Aaron⁵  Magagi, Ramata⁶  Gao, Ying^7,8  Bindlish, Rajat⁹  Williamson, Ross¹  Ramos, Isaac¹  Latham, Barron¹  O'Neill, Peggy⁹  Yueh, Simon¹ 

[1] CALTECH, Jet Prop Lab, Pasadena, CA 91125 USA

[2] USDA ARS, Hydrol & Remote Sensing Lab, Beltsville, MD USA

[3] Agr & Agri Food Canada, Burnaby, BC, Canada

[4] Univ Manitoba, Winnipeg, MB, Canada

[5] Univ Guelph, Guelph, ON, Canada

[6] Univ Sherbrooke, Sherbrooke, PQ, Canada

[7] Monash Univ, Clayton, Vic, Australia

[8] UCLA JIFRESSE, UCLA Joint Inst Reg Earth Syst Sci & Engn, Los Angeles, CA USA

[9] NASA, Goddard Space Flight Ctr, Greenbelt, MD USA

关键词: SMAPVEX16;    PALS;    SMAP;    Soil moisture;    Satellite remote sensing;    Aircraft remote sensing;    In situ instrumentation;   

DOI  :  10.1016/j.rse.2019.04.004

来源: Elsevier

【 摘 要 】

The NASA's Soil Moisture Active Passive (SMAP) mission conducted a field experiment with its partners over two 40-km agricultural domains in Iowa and Manitoba in the summer of 2016 to address concerns observed in SMAP soil moisture (SM) retrievals over agricultural areas. The experiment featured airborne Passive Active L-band System (PALS) flights over each domain with intensive ground measurements and dense networks of SM monitoring stations. With two intensive observation periods separated in time (May 28 June 20 and July 14 August 16), the flights captured both early-season/low vegetation and later-season/high-vegetation conditions. The comparison of the PALS brightness temperature (TB) measurements to the SMAP TB observed over the sites resulted in root mean square difference (RMSD) of 2.8 K and 4.0 K for vertical and horizontal polarizations, respectively. The subsequent SM analysis resealed the PALS TB with the SMAP TB to allow equitable comparisons between the SM retrievals from the two instruments. The PALS SM retrieval algorithm used the SM sampled by the ground teams during the overpass days for tuning, and was parameterized by a high-resolution vegetation water content product calibrated using vegetation samples collected during the experiment. The tuning process was not able to find a satisfactory result with a temporally constant set of parameters in the single channel algorithm for the two intensive observation periods of the experiment. This result indicated that the rapid change in the vegetation structure during the growth stages and likely variation in the surface roughness conditions were not compatible with rigid parameterization over the entire period. However, using seasonally variable parameters we found that it was possible to retrieve soil moisture with satisfactory accuracy. Comparative analysis with the SMAP SM product included aggregation of the PALS SM to the SMAP pixel-scale. The RMSD between the PALS SM and the aggregated manual field samples was < 0.04 m(3)/m(3) with Pearson correlation > 0.85 for both sites. The comparison between different in situ sources indicated that the soil moisture network measurements were not the source of the large biases observed for SMAP over the sites reported in earlier studies. Therefore, the results suggested the rapidly growing vegetation and the early-season surface condition changes not captured by the SMAP algorithm caused the SMAP retrieval errors. In addition, the significant deviations of the vegetation water content used by the SMAP product from the calibrated vegetation water content obtained during the experiment compounds the problem.

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