The soil moisture active passive experiments (SMAPEx): Towards soil moisture retrieval from the SMAP mission

Authors: PANCIERA, ROCCO - University Of Melbourne; WALKER, JEFFREY - Monash University; Jackson, Thomas; RYU, DONGRYEOL - University Of Melbourne; GRAY, DOUG - University Of Adelaide; MONERRIS, ALESSANDRA - Monash University; YARDLEY, HEATH - University Of Adelaide; TANASE, MIHAI - University Of Melbourne; RUDIGER, CHRIS - Monash University; WU, XIAOLING - Monash University; GAO, YING - Monash University; HACKER, JORG - Flinders University

Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2013
Publication Date: 1/2/2014
Publication URL: https://handle.nal.usda.gov/10113/59870
Citation: Panciera, R., Walker, J.P., Jackson, T.J., Ryu, D., Gray, D., Monerris, A., Yardley, H., Tanase, M., Rudiger, C., Wu, X., Gao, Y., Hacker, J. 2014. The soil moisture active passive experiments (SMAPEx): Towards soil moisture retrieval from the SMAP mission. IEEE Transactions on Geoscience and Remote Sensing. 52:490-507.

Interpretive Summary: The Soil Moisture Active Passive Experiments (SMAPEx) were successfully conducted over diverse landscapes, phonological conditions, and soil moisture levels in an agricultural region of Australia. The most pressing research question to be addressed before the launch of the Soil Moisture Active Passive (SMAP) satellite is the development and testing of techniques to fuse the radar and radiometer measurements to obtain a combined soil moisture product at intermediate spatial resolution; however, there are few data sets available that can be used for this purpose. This series of three airborne field experiments using SMAP instrument simulators will be used for the development and validation of soil moisture retrieval. The SMAPEx dataset represents an important contribution to development of the SMAP mission serving as an extensive and valuable test bed to address the variety of SMAP pre-launch science questions. SMAP products will impact applications in agricultural hydrology, drought, flood, and climate analyses.

Technical Abstract: NASA’s Soil Moisture Active Passive (SMAP) mission, scheduled for launch in 2014, will carry the first combined L-band radar and radiometer system with the objective of mapping near surface soil moisture and freeze/thaw state globally at near-daily time step (2-3 days). SMAP will provide three soil moisture products; high resolution from radar (~3 km), low resolution from radiometer (~36km), and intermediate resolution from the fusion of radar and radiometer (~9 km). The Soil Moisture Active Passive Experiments (SMAPEx) are a series of three airborne field experiments specifically designed to provide prototype SMAP data, for the development and validation of soil moisture retrieval algorithms applicable to the SMAP system configuration and resolutions. This paper describes the SMAPEx sampling strategy and presents an overview of the data collected during the three experiments, SMAPEx-1 (July 5-10, 2010), SMAPEx-2 (December 4-8, 2010) and SMAPEx-3 (Sept 5-23, 2011). The SMAPEx experiments were conducted in a semi-arid agricultural area located in southeastern Australia, timed so as to acquire data over a seasonal cycle at various stages of the crop growing season. Airborne L-band brightness temperature (~1km) and radar backscatter (~10m) observations were collected over an area the size of a single SMAP footprint (38km × 36km at 35° latitude) with 2-3 days revisit time, providing SMAP-like data for testing of radiometer-only, radar-only, and combined radiometer-radar soil moisture retrieval and downscaling algorithms. Additional SMAPEx flights targeted issues specifically related to radar sensing, i.e., the scaling of radar observations with resolution and the impact of incidence and azimuth angle on the scattering coefficients. Airborne observations were supported by continuous monitoring of near-surface (0-5cm) soil moisture at a network of 29 sites, and intensive ground monitoring of soil moisture, soil temperature, vegetation biomass and structure, and surface roughness across six 3km × 3km focus areas. The data described in this paper are available at www.smapex.monash.edu.au