A physically-based inversion algorithm for retrieving soil moisture in passive microwave remote sensing

► By reducing degrees of freedom of the Fresnel equation, a unique inversion algorithm (Hong’s algorithm) is developed for retrieving soil moisture in passive microwave remote sensing. ► The surface roughness and the dielectric constant are retrieved using Hong’s approximation. ► The Hong’s algorith...

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Vydáno v:	Journal of hydrology (Amsterdam) Ročník 405; číslo 1; s. 24 - 30
Hlavní autoři:	Hong, Sungwook, Shin, Inchul
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	Kidlington Elsevier B.V 21.07.2011 Elsevier
Témata:	Algorithms Applied geophysics Dielectric constant Earth Observing System Earth sciences Earth, ocean, space energy equations Exact sciences and technology Georgia Hong’s approximation Hydrology Hydrology. Hydrogeology Internal geophysics Inversion Inversions land use Mathematical analysis Microwaves Missions oceans Oklahoma Polarization radiometers Remote sensing Retrieval roots Roughness salinity satellites Soil moisture soil water surface roughness temperature Volumetric soil water content United States Oklahoma Georgia USA, Oklahoma ASW, USA, Georgia Polarization Inversion Dielectric constant Hong’s approximation Volumetric soil water content Roughness atmosphere microwaves algorithms accuracy soil water North America dielectric constant roughness water content polarization soils satellites models inverse problem salinity interfaces soil moisture Space remote sensing Hong's approximation surface water brightness temperature errors Pixel
ISSN:	0022-1694, 1879-2707
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Shrnutí:	► By reducing degrees of freedom of the Fresnel equation, a unique inversion algorithm (Hong’s algorithm) is developed for retrieving soil moisture in passive microwave remote sensing. ► The surface roughness and the dielectric constant are retrieved using Hong’s approximation. ► The Hong’s algorithm shows good consistency with field observations (SMEX03) and with current AMSR-E soil moisture algorithms. ► Consequently, the Hong’s algorithm is advantageous for an operational purpose with the minimal use of land surface forward models. Surface soil moisture plays a key role in water and energy exchanges at the land–atmosphere interface. Previous research on the microwave remote sensing of soil moisture focused mostly on the forward modeling problem. This paper presents a unique inversion algorithm (Hong’s algorithm) for soil moisture retrieval with reduced degrees of freedom of the Fresnel equation; the algorithm is based on the characteristics of the polarization ratio for rough surfaces around the Brewster angle and Hong’s approximation, which is an approximate relationship between vertically and horizontally polarized reflectivities. Using the daily observations of the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) taken at 0.25° × 0.25° pixel, the soil moisture is estimated globally over the land surface using a relation between the complex dielectric constant and the soil moisture after retrieving the surface roughness and complex dielectric constant. The surface soil moisture products obtained from Hong’s algorithm are validated using in situ observations carried out in Oklahoma and Georgia in 2003. The official AMSR-E soil moisture products are compared to assess Hong’s algorithm using identical brightness temperature data sets. The biases and the root mean squared error calculated in comparison with the ground observations are in the range of −0.059 m 3/m 3 to 0.01 m 3/m 3 and 0.023 m 3/m 3 to 0.065 m 3/m 3, respectively. Hong’s algorithm estimates the soil moisture within the estimated accuracy of AMSR-E surface soil moisture, 0.06 m 3/m 3, without requiring a priori information about the roughness and the dielectric constants of the surface. With a minimal use of forward models, this research could also be applied to global soil moisture retrieval in the Soil Moisture and Ocean Salinity satellite mission and the Soil Moisture Active/Passive mission.
Bibliografie:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0022-1694 1879-2707
DOI:	10.1016/j.jhydrol.2011.05.005