Evaluation of MERRA Land Surface Estimates in Preparation for the Soil Moisture Active Passive Mission

• Published in: Journal of climate Vol. 24; no. 15; pp. 3797 - 3816
• Main Authors: Yi, Yonghong, Kimball, John S., Jones, Lucas A., Reichle, Rolf H., McDonald, Kyle C.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.08.2011
• Subjects: Accuracy; Air temperature; Algorithms; Data processing; Datasets; Earth, ocean, space; Exact sciences and technology; External geophysics; Forest soils; Hydrologic cycle; In situ measurement; Latitude; Meteorology; Microwaves; Mountain regions; Precipitation; Remote sensing; Soil moisture; Soil surfaces; Soil temperature regimes; Soil water; Solar radiation; SPECIAL MERRA COLLECTION; Surface temperature; Tropical forests; Tropical regions; Vapor pressure; Weather; High latitude; Mid latitude; Meteorological observation; soil moisture; Vapor pressure; atmospheric precipitation; Space remote sensing; Satellite observation; solar radiation; Surface temperature; vegetation; Tropical forest; Advanced microwave scanning radiometer; cartography; Freeze thaw cycle; Measurement in situ; deserts; Atmospheric temperature; Ground surface; Cloudiness; Reanalysis; Low latitude; Microwave radiometry
• ISSN: 0894-8755; 1520-0442; 1520-0442
• DOI: 10.1175/2011jcli4034.1

The authors evaluated several land surface variables from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) product that are important for global ecological and hydrological studies, including daily maximum (T max) and minimum (T min) surface air temperatures, atmosphere vapor pressure deficit (VPD), incident solar radiation (SWrad), and surface soil moisture. The MERRA results were evaluated against in situ measurements, similar global products derived from satellite microwave [the Advanced Microwave Scanning Radiometer for Earth Observing System (EOS) (AMSR-E)] remote sensing and earlier generation atmospheric analysis [Goddard Earth Observing System version 4 (GEOS-4)] products. Relative to GEOS-4, MERRA is generally warmer (∼0.5°C forT minandT max) and drier (∼50 Pa for VPD) for low- and middle-latitude regions (<50°N) associated with reduced cloudiness and increased SWrad. MERRA and AMSR-E temperatures show relatively large differences (>3°C) in mountainous areas, tropical forest, and desert regions. Surface soil moisture estimates from MERRA (0–2-cm depth) and two AMSR-E products (∼0–1-cm depth) are moderately correlated (R∼ 0.4) for middle-latitude regions with low to moderate vegetation biomass. The MERRA derived surface soil moisture also corresponds favorably with in situ observations (R= 0.53 ± 0.01,p< 0.001) in the midlatitudes, where its accuracy is directly proportional to the quality of MERRA precipitation. In the high latitudes, MERRA shows inconsistent soil moisture seasonal dynamics relative to in situ observations. The study’s results suggest that satellite microwave remote sensing may contribute to improved reanalysis accuracy where surface meteorological observations are sparse and in cold land regions subject to seasonal freeze–thaw transitions. The upcoming NASA Soil Moisture Active Passive (SMAP) mission is expected to improve MERRA-type reanalysis accuracy by providing accurate global mapping of freeze–thaw state and surface soil moisture with 2–3-day temporal fidelity and enhanced (≤9 km) spatial resolution.