摘要
本文提出一种采用NOAA卫星AVHRR和地形高度等资料,估算流域蒸散的方法。NOAA AVHRR资料用于地表覆盖分类,据此可得出各类下垫面由可能蒸发转换成实际蒸散的折算因子。该资料还可用于计算地面反射率和气温,本文利用与卫星象元相匹配的1.2'经纬度网格上的海拔高度资料将流域内少数气象站观测的气象要素作为高度的函数插到此网格上,然后用改进的彭曼模式计算了甘肃省河西内陆河10个流域中各类下垫面的蒸散和蒸发。然后与少数雪面和高山草甸区实测的资料以及用水份平衡方法估算的相应流域的蒸散比较,验证了用此方法估算逐月流域蒸散量的可靠性。
Accurate estimation of ET over large areas, such as the watershed of a river is a problem to be solved. ET depends on variousparameters such as physical characteristics of ground surface. Land cover categories include glaciers, seasonal snows rocks, alpine grasslands, forestry deserts and oases. It seems unrealistic that direct measurements of these parameters could be performed. Remote sensing may provide surface information simultaneuosly and homogeneously over large areas for estimating some of the factors controlling surfcae ET. In this paper, an overall improved Penmen model has been used, A method to estimate monthly actual ET over river basin with complex terrain and various land cover categories has been developed.
The model for estimating ET consists of three procedures. The first one is apreparatory step including using data, determining the river basin boundary, amending and interpolating AVHRR data at the mesh scale of 1.2' in latitude by 1.2' in longitude after normalizing NOAA-9 data, from albedo of channel 1 and channel 2 to NOAA-10 using empirical formulas. Meteorological data which offer all other necessary information for estimating ET are input into the computer. The second step is executing the program, inputting the elevations of the Qilian Mountain at the same mesh size as the AVHRR data, classifying the area into cloudiness, snow cover, rock, vegetation, bare soil, desert and water by using Chen Tia-nyu and Chen Qian's method. Then every planetary albedo under different land covers is derived form channels 1 and 2 based on a statistical method given in the technical report of NOAA NESDIS NO. 27, Surface albedo can be derived from the planetary albedo by Zhong Qiang's method (1988). Brightness temperature (TB) was trans lated to air temperature at 1.5 m high over various land cover categories by using Guo Ni and Chen Qian's method (1991). Each meteorological element is regressed linearly with elevation. Each element at every grid point is a function of elevation. When the elevation is more than 3500 m, the air temperatures are mainly retrieved from TB of channel 4. The improved Penmen model used to estimate potential evaporation (EC) for each land cover category based on the observation of radiation budget over the Qinghai-Xizang plateau is as follow:
Where f(u is the function of wind speed; U2 is the average wind speed above surface 2 meters; e, is saturated vapor pressure; ed is vapor pressure; R, is surface net radiation; as is surface albedo; Q0 is total solar radiation on surface under clear conditions and Q is under cloudy; a is regression coefficient; n is duration of sunshine; N is daytime hours; F is effective radiation; 8 is surface emissivity; a is Stefan-Boltzmann's constant; T, is air temperature; W is vapor content in column; Z is elevation (km); A is changeable rate of saturation vapor pressure with temperature; and r is humdity constant in Bowen ratio equation. In the third step, by using Pristley-Taylor factor method (1972) the potential evaporation EC can be converted into the actual evaporation or evapotranspiration ET.
ET = C X EC (7)
where C is Pristley-Taylor factor, which varies with land cover categories. Based on different empirical formulas C can be obtained.
Based on above-mentioned model, for five kinds land cover categories, monthlyactual evaporations or evapotranspirations from Danghe River to Zamuhe River basins have been estimated during March to May 1987 and March to April 1988. We have the observational evaporations in snow cover and ET in alpine grass surface recorded at a few station obtained by weighing method, which are close to the calculating values. Comparing with the results from the same river basins obtained by means of the water balance method, the relative errors of this method are from?5.0% to 12.2%, and the average value equals to?.36%. Ina large basins the errors are smaller, such as in Danghe River and Changmahe River basins over 0.23% and 5.17%. The errors are large over small river basins especially in Huongshibahe River and Liyuanhe Rive
出处
《地理学报》
EI
CSSCI
CSCD
北大核心
1993年第1期61-69,共9页
Acta Geographica Sinica
基金
本工作得到甘肃省自然科学基金资助。
关键词
流域蒸散
卫星资料
复杂地形
River basin evapotranspiration
AVHRR data
Land cover category
