BAYESIAN COMBINED ACTIVE/PASSIVE (B-CAP) SOIL MOISTURE RETRIEVAL ALGORITHM: A RIGOROUS RETRIEVAL SCHEME FOR SMAP MISSION
IGARSS 2015 – Remote Sensing: Understanding the Earth for Safer Word – July 26-31, Milan, Italy
Abstract:
On-going and near-future Synthetic Aperture Radar (SAR) satellite missions are expected to provide meaningful and timely information about soil condition over vast agricultural lands such as those of Argentina (Pampas Plain) and of the mid-western United States (corn-belt), leading to actual economic benefits regarding to seeding dates, irrigation strategies and crop yield forecasting. NASA’s Soil Moisture Active and Passive (SMAP) [1] and Argentinean SAOCOM (www.conae.gov.ar) missions have been specifically designed to develop surface soil moisture products and they are scheduled for launch in January 2015 and late 2015, respectively. These missions will exploit microwave radar at L-band (λ = 23cm) as sensing wavelength, which demonstrated to be less sensitive to residue cover over soil’s surface and to be more accurate on retrieving soil moisture than other bands.
In addition to microwave radar, microwave radiometry is also a well-established technique for remote sensing of soil moisture. Combining passive and active observations provides complementary information contained in the surface emissivity and backscatter signatures, both correlated to soil dielectric properties. When active and passive microwave information are available at the same resolution, a Bayesian merging technique can be used to retrieve enhanced, combined active passive soil moisture estimations from remotely-sensed microwave observations.
We present here a Bayesian active/passive methodology in which soil moisture estimations from passive microwave data is used to constrain the estimation from active radar ones through a preliminary soil moisture guess, provided active and passive observations are made at the same resolution. This methodology exploits outstanding, rigorous IEM2M as forward model [2] to describe radar rough-surface scattering of bare or sparsely-vegetated soils and can be regarded as a benchmark to test SMAP active/passive soil moisture product over agricultural lands. The capability of passive microwave measurements to improve radar soil moisture predictions is demonstrated in this paper with in-situ and airborne observations from Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEx12) field campaign.