Dr. Yang Le Profile

Dr. Yang Le

at Institute of Remote Sensing and Digital Earth

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Proceedings Article | 21 November 2012 Paper

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

Le Yang, Qinhuo Liu

Proceedings Volume 8524, 85240Q (2012) https://doi.org/10.1117/12.977341

KEYWORDS: Backscatter, Radar, Aerodynamics, Surface roughness, Vegetation, Microwave radiation, Scattering, Soil science, Ku band, Remote sensing

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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.

Proceedings Article | 19 October 2012 Paper

Investigation of the difference between thermal infrared canopy temperature and microwave effective canopy temperature over homogeneous corn canopy

Jing Liu, Qinhuo Liu, Hongzhang Ma, Le Yang, Jingjing Peng

Proceedings Volume 8531, 85311Y (2012) https://doi.org/10.1117/12.971451

KEYWORDS: Infrared radiation, Thermography, Microwave radiation, L band, Polarization, Vegetation, Thermal modeling, Soil science, Multiple scattering, Infrared sensors

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Land surface temperature (LST) is an important parameter that modulates land surface process. The combination of infrared temperature and microwave temperature is a trend in the research of LST. Thermal infrared temperature and microwave temperature have different physical significances and values. However, they are always treated as the same temperature nowadays in the research on the combination of infrared temperature and microwave temperature. In this study, the homogeneous canopy is the leaf-dominated crown layer ignoring the effect of branches. Two layers with different temperature, the canopy layer and the soil layer, are considered. MESCAM model based on matrix doubling method has been modified by getting rid of the effects of the main and secondary stems. The effect of multiple scattering at L and C band has been studied by comparing the results of taoomiga model with that of the modified MESCAM model. Tao-omiga model was adopted to compute the canopy brightness temperature at L band and a simple geometric-optical model basing on gap probabilities was used to compute the canopy brightness temperature at thermal infrared band in the same scene. The relationship and the difference between thermal infrared canopy surface physical temperature and L band canopy effective physical temperature with different soil moisture have been analyzed in three different situations of T_C (the temperature of the foliage component) and T_S (the temperature of the soil component). It is a base of further exploring the cooperative inversion combining thermal infrared remote sensing with passive microwave remote sensing.

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