Abstract:
NASA's Soil Moisture Active Passive (SMAP) Mission is scheduled for launch in October 2014. The objective of the mission is global mapping of soil moisture and freeze/thaw state. SMAP utilizes an L-band radar and radiometer sharing a rotating 6-meter mesh reflector antenna. The instruments will operate onboard the SMAP spacecraft in a 685-km Sun-synchronous near-polar orbit, viewing the surface at a constant 40-degree incidence angle with a 1000-km swath width. Merging of active and passive L-band observations of the mission will enable an unprecedented combination of accuracy, resolution, coverage and revisit-time for soil moisture and freeze/thaw state retrieval. SMAP measurements will enable significantly improved estimates of water, energy and carbon transfers between the land and atmosphere. The SMAP science data product suite of geophysical parameters will include estimates of surface (top 5 cm) and root-zone (down to 1-m depth) soil moisture, net ecosystem exchange, and classification of the frozen/non-frozen state of the landscape. The primary validation reference of the data products will be ground-based measurements. Other remote sensing and model-based products will be used as additional resources. The post-launch timeline of the mission requires that the geophysical data products are validated (with respect to the mission requirements) within 12 months after a 3-month in-orbit check-out phase. SMAP is taking several preparatory steps in order to meet this schedule. One of the main steps consists of running a rehearsal to exercise calibration and validation procedures planned for the Cal/Val Phase. The rehearsal is divided into two stages. Phase 1, which was conducted in June-August 2013, focused on validation methodologies for the geophysical data products. Phase 2, which will be conducted in May-June 2014, includes operational aspects including a fully functioning SMAP Science Data System. (Note that the rehearsals do not include an airborne field campaign.) Phase 1 of the rehearsal included: generation of simulated SMAP data products; establishing automated data transfers of both small-scale, dense and large-scale, sparse in situ networks operated by a subset of SMAP Cal/Val Partners; exercising of in situ data transfer protocols, and in situ data formatting, comparison and metric computation tools; and running inter-comparisons between the simulated products and other satellite and model-based products. The comparisons were made with data from a period starting in May 2013 and accumulated during the course of the activity, which forced the exercise of obtaining and processing recently acquired data. A large part of the time was devoted to establishing data transfers from the Cal/Val Partners. Phase 1 produced a list of actions and lessons learned which will be implemented by Phase 2 of the rehearsal to improve the Cal/Val procedures and readiness as the mission moves toward launch.