[求助]从遥感卫星地面站LANDSAT5TM数据怎么计算地表发射率

小弟曾从中国遥感卫星地面站买过LANDSAT5的TM数据，现在需要求一下地表发射率。所购买数据是TML4级产品，网站介绍说已经过辐射校正，但是也不知道用什么方法做的，打电话问他们说是经过辐射纠正，用软件做的，具体用哪种方法，做到哪一步，有没有经过大气校正也不清楚，叫我查美国USGS网，结果也没搞清楚。<BR>我用NEVI打开某波段快速统计显示的是DN值，最大255 最小是0 。头文件内容为：<BR>PRODUCT =08353905-01 WRS =121/03600 ACQUISITION DATE =20080601 SATELLITE =L5 INSTRUMENT =TM10 PRODUCT TYPE =MAP ORIENTED   PRODUCT SIZE =SUB SCENE                                                                                TYPE OF GEODETIC PROCESSING =PRECISION  RESAMPLING =CC RAD GAINS/BIASES =  0.99992/-0.0100  2.42430/-0.0232  1.36344/-0.0078  2.62901/-0.0193  0.58771/-0.0080  3.20107/0.25994  0.38674/-0.0040 VOLUME #/# IN SET =1/1 START LINE #=    1 LINES PER VOL=56497 ORIENTATION = -0.00 PROJECTION =TM   USGS PROJECTION # =     9 USGS MAP ZONE =     0 USGS PROJECTION PARAMETERS = 6378245.000000000000000 6356863.018773047300000       1.000000000000000       0.000000000000000     116.999987117997050       0.000000000000000  500000.000000000000000       0.000000000000000       0.000000000000000       0.000000000000000       0.000000000000000       0.000000000000000       0.000000000000000       0.000000000000000       0.000000000000000 EARTH ELLIPSOID =Krassovsky           SEMI-MAJOR AXIS =6378245.000 SEMI-MINOR AXIS =6356863.019 PIXEL SIZE =25.00 PIXELS PER LINE= 4583 LINES PER IMAGE= 8071 UL 1164656.1881E 353148.6330N    480252.940   3933505.023 UR 1180243.6983E 353133.0280N    594827.940   3933505.023 LR 1180122.4827E 334226.2410N    594827.940   3731730.023 LL 1164713.1052E 334240.8273N    480252.940   3731730.023 BANDS PRESENT =1234567 BLOCKING FACTOR =   1 RECORD LENGTH = 4583 SUN ELEVATION =66 SUN AZIMUTH =114 CENTER 1172433.1364E 343713.5967N    537527.952   3832630.113  2291  4035 OFFSET=-129 REVB<BR>请问如何根据提供的影像计算地表发射率。小弟初学，恳请高手指点，不胜感激，叩谢。