Microwave Land Emissivity Calculations over the Qinghai-Tibetan Plateau Using FY-3B/MWRI Measurements

Ying Wu,Yansong Bao,Xulin Liu,George P Petropoulos,Bo Qian,Lin Li

doi:10.3390/rs11192206

Abstract

The Qinghai-Tibetan plateau plays an important role in climate change with its unique characteristics, and the surface emissivity is an important parameter to describe the surface characteristics. It is also very important for the accurate retrieval of surface and atmospheric parameters. Different types of surface features have their own radiation characteristics due to their differences in structure, water content and roughness. In this study, the microwave land surface emissivity (10.65, 18.7, 23.8, 36.5 and 89 GHz) of the Qinghai-Tibetan Plateau was calculated using the simplified microwave radiation transmission equation under clear atmospheric conditions based on Level 1 brightness temperatures from the Microwave Radiation Imager onboard the FY-3B meteorological satellite (FY-3B/MWRI) and the National Centers for Environmental Prediction Final (NCEP-FNL) Global Operational Analysis dataset. Furthermore, according to the IGBP (International Geosphere-Biosphere Program) classified data, the spectrum and spatial distribution characteristics of microwave surface emittance in Qinghai-Tibetan plateau were further analyzed. The results show that almost all 16 types of emissivity from IGBP at dual-polarization (vertical and horizontal) increase with the increase of frequency. The spatial distribution of the retrieving results is in line with the changes of surface cover types on the Qinghai-Tibetan plateau, showing the distribution characteristics of large polarization difference of surface emissivity in the northwest and small polarization difference in the southeast, and diverse vegetation can be clearly seen in the retrieving results. In addition, the emissivity is closely related to the type of land surface. Since the emissivity of vegetation is higher than that of bare soil, the contribution of bare soil increases and the surface emissivity decreases as the density of vegetation decreases. Finally, the source of retrieval error was analyzed. The errors in calculating the surface emissivity might mainly come from spatiotemporal collocation of reanalysis data with satellite measurements, the quality of these auxiliary datasets and cloud and precipitation pixel discrimination scheme. Further quantitative analysis of these errors is required, and even standard procedures may need to be improved as well to improve the accuracy of the calculation.

Highlights

Land surface emissivity in the microwave region is an important parameter in both the assimilation of microwave radiation data and the retrieval of surface and atmospheric parameters from satellite microwave measurements [1,2,3]
The characteristics of surface emissivity in the study area were compared with the ground coverTdhaetcah. aTrhaectseurirsftaicse ocfosvuerfaagcee demataissuisveidtyiinntthhies ssttuuddyyawreearewferoremcothmepMarWedRwI Litahntdhceogvreorudnadtacosevtesr, idnawtah. iTcheIGsuBrPfalacnedcosvuerfracgeecdoavtearaugseedaitna athti8s9sGtuHdzy awreersetofrreodmwtihthe aMhWorRizIoLnatanldrceosovleurtidoantaosfe9tsk, min ×w1h5ickhmIG(BFiPgularned3)s.uArfasctehecosvaeterallgitee dpaatsaseadt 8o9vGerHthzeasretusdtoyrreedgwiointhona hthoeriszcoanntnalinrgesorlubitti,otnhoefs9urkfmace× c1o5vkermag(eFtiygpueres f3r)o.mAtshtehneosrathtewlleitset tpoatshsedsoouvthereatshteosfttuhdeyQrinegihoani-ToinbetthaensPclaantenainugchoarnbgite,dthfreosmurbfarcee coverage types from the northwest to the southeast of the Qinghai-Tibetan Plateau changed from bare or semi-desert to grassland with trees, prairie, permanent wetlands, grassland with trees, deciduous broadleaved forest and evergreen broadleaved forest (Figure 3 and Table 2)
The Qinghai-Tibetan Plateau plays an important role in climate change because of its unique characteristics

Summary

Introduction

Land surface emissivity in the microwave region is an important parameter in both the assimilation of microwave radiation data and the retrieval of surface and atmospheric parameters from satellite microwave measurements [1,2,3]. Based on the microwave radiative transfer equation, Wilke and McFarland assumed an approximate atmospheric transmittance equal to unity in clear skies and ignored the influence of clouds. With these assumptions, the land surface emissivity is the ratio of the microwave brightness temperature from the satellite and the skin temperature of the land surface [13]

Objectives

Results

Conclusion