Analysis of microwave backscatter measured by radar altimeter on land to study surface aerodynamic roughness

Le Yang; Qinhuo Liu

doi:10.1117/12.977341

21 November 2012 Analysis of microwave backscatter measured by radar altimeter on land to study surface aerodynamic roughness

Le Yang, Qinhuo Liu

Author Affiliations +

Proceedings Volume 8524, Land Surface Remote Sensing; 85240Q (2012) https://doi.org/10.1117/12.977341
Event: SPIE Asia-Pacific Remote Sensing, 2012, Kyoto, Japan

Abstract

The aerodynamic surface roughness z0 is a key parameter for climate and land-surface models to study surfaceatmosphere exchanges of mass and energy. The roughness length is difficult to estimate without wind speed profile data, which is intractable at regional to global scale. Theoretical formulations of roughness have been developed in terms of canopy attributes such as frontal area, height, and drag coefficient. This paper discusses the potential of radar altimetry, which provides the backscatter coefficient of the land surface at nadir view, to characterise the surface roughness at km scale. The AIEM model and ProSARproSIM are employed to simulate the backscatter coefficient under different surface condition and different observation geometry at bare soil and at pine forest, respectively. The altimetry backscatter decreases with increase of geometric roughness. The microwave backscatter measured at the nadir view is more sensitive to the surface roughness than that at the oblique observation, especially for the smooth surface. The direct forest return is the dominated scattering mechanism for normal incidence at forest area. Since we failed to collect the z0 measurement at arid and semi-arid area with sparse vegetation, the backscatter measurements at Ku and C band of altimeter Jason1 were analyzed with the ground measured aerodynamic surface roughness at three vegetated sites (Da yekou, Yin ke, and Chang Baisan) of China. The relationships we found between Jason1 sigma0 and z0 is not significant, since Jason1 lost track seriously at the three sites. Further research using the altimeter data of Jason2 and Cryosat is possible to demonstrate the potential to map z0 from orbit using radar altimeters.

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Le Yang and Qinhuo Liu "Analysis of microwave backscatter measured by radar altimeter on land to study surface aerodynamic roughness", Proc. SPIE 8524, Land Surface Remote Sensing, 85240Q (21 November 2012); https://doi.org/10.1117/12.977341

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KEYWORDS

Backscatter

Aerodynamics

Radar

Surface roughness

Vegetation

Microwave radiation

Scattering

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