Abstract
Abstract. In this study, a parameterization method based on MODIS (Moderate Resolution Imaging Spectroradiometer) data, AVHRR (Advanced Very High-Resolution Radiometer) data and in situ data is introduced and tested for estimating the regional evaporative fraction Λ over a heterogeneous landscape. As a case study, the algorithm was applied to the Tibetan Plateau (TP) area. Eight MODIS data images (17 January, 14 April, 23 July and 16 October in 2003; 30 January, 15 April, 1 August and 25 October in 2007) and four AVHRR data images (17 January, 14 April, 23 July and 16 October in 2003) were used in this study to compare winter, spring, summer and autumn values and for annual variation analysis. The results were validated using the "ground truth" measured at Tibetan Observation and Research Platform (TORP) and the CAMP/Tibet (CEOP (Coordinated Enhanced Observing Period) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau) meteorological stations. The results show that the estimated evaporative fraction Λ in the four different seasons over the TP is in clear accordance with the land surface status. The Λ fractions show a wide range due to the strongly contrasting surface features found on the TP. Also, the estimated Λ values are in good agreement with "ground truth" measurements, and their absolute percentage difference (APD) is less than 10.0% at the validation sites. The AVHRR data were also in agreement with the MODIS data, with the latter usually displaying a higher level of accuracy. It was therefore concluded that the proposed algorithm was successful in retrieving the evaporative fraction Λ using MODIS, AVHRR and in situ data over the TP. MODIS data are the most accurate and should be used widely in evapotranspiration (ET) research in this region.
Highlights
As the most prominent and complicated terrain on the earth, the Tibetan Plateau (TP) makes up approximately one quarter of the land area of China, stretching from the Pamir Plateau and Hindu-Kush in the west to the Hengduan Mountains in the east, and from the Kunlun and Qilian mountains in the north to the Himalayas in the south
The most relevant in situ data, collected at the key Tibetan Observation and Research Platform (TORP) stations in the TP to support the parameterization of the evaporative fraction and analysis of the Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High-Resolution Radiometer (AVHRR) images, consist of surface radiation budget components, surface radiation temperatures, surface reflectance, vertical profiles of air temperature, humidity, wind speed and direction measured at atmospheric boundary layer (ABL) towers, wind profiler and RASS, radiosonde and tether sonde, turbulent fluxes measured by eddy-correlation technique, soil heat flux, soil temperature profiles, soil moisture profiles, and the vegetation state
The most relevant in situ data, collected at the D105, NPAM and ANNI CAMP/Tibet stations (Ma et al, 2005) over the TP to support the parameterization of the evaporative fraction and analysis of MODIS and AVHRR images, consist of surface radiation budget components, surface radiation temperatures, surface reflectance, vertical profiles of air temperature, humidity, automatic weather station (AWS)-recorded wind speed and direction, soil heat flux, soil temperature profiles, soil moisture profiles, and the vegetation state
Summary
As the most prominent and complicated terrain on the earth, the Tibetan Plateau (TP) makes up approximately one quarter of the land area of China, stretching from the Pamir Plateau and Hindu-Kush in the west to the Hengduan Mountains in the east, and from the Kunlun and Qilian mountains in the north to the Himalayas in the south. We found that the evaporative fraction remained nearly constant from sunrise to sunset during clear days at the Tibetan Observation and Research Platform stations (TORP, Ma et al, 2008), dependent upon land surface types (see Fig. ). Wang et al (2006) estimated from a combination of day and night land surface temperatures and the Normalized Difference Vegetation Index (NDVI). This is the first deliberative study of the evaporative fraction over the heterogeneous landscape of the whole TP. The regional distribution of the evaporative fraction over the TP will be both estimated and validated in this study
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
