表觀反射率(反射率、反照率)的計算

1、表觀反射率（反射率、反照率）的計算表觀反射率（反射率、反照率）的計算第一步、分別計算各個波段每個像元的輻射亮度L值：L=GainDNBias或者minminminmaxminmax)(LQCALQCALQCALQCALLLL?????式中，QcaL為某一像元的DN值，即QCAL=DN。QCALmax為像元可以取的最大值255。QCALmin為像元可以取的最小值。如果衛(wèi)星數(shù)據(jù)來自LPGS(Thelevel1productgeneratio

2、nsystem)，則QCAL=1(Lsat7數(shù)據(jù)屬于此類型)。如果衛(wèi)星數(shù)據(jù)來自美國的NLAPS(NationalLsatArchiveProductionSystem)，則QCALmin=0(Ldsat5的TM數(shù)據(jù)屬于此類型)。根據(jù)以上情況，對于Lsat7來說，可以改寫為(QCALmin=1)：minminmax)1(254LDNLLL????對于Lsat5來說，可以改寫為(QCALmin=0)：minminmax255LDNLLL??

3、?表1Isa7ETM各個反射波段的Lmax和Lmin值Table1ThevaluesofLmmaxLminfreflectingbsofLsat7ETM(W˙m2sr1˙μm1)2000年7月1日之前2000年7月1日之后低Gain高Gain低Gain高Gain波段BLminLmaxLminLmaxLminLmaxLminLmax16.2297.56.2194.36.2293.76.2191.626.0303.46.0202.46.43

4、00.96.4196.534.5235.54.5158.65.0234.45.0152.944.5235.54.5157.55.1241.15.1157.451.047.71.031.761.047.571.031.0670.3516.60.3510.9320.3516.540.3510.8表2Lsat5TM各反射波段的Lmax和Lmin值Table2ThevaluesofLmaxLminfreflectingbsofLsat5TM(W

5、˙m2sr1˙μm1)19840301至2003050420030504之后波段BLminLmaxLminLmax11.52152.101.52193.022.84296.812.84365.031.17204.301.17264.041.51206.201.51221.050.3727.190.3730.2波段B123457Lsat7ESUN1969184015511044225.782.07Lsat5ESUN195718261554

6、103621580.67兩步合為一步計算如下：波段）為第iiLQCALQCALQCALQCALLLCosESUNDxmai()()(minminminmaxmin2?????????????????對于Lsat7上試簡化為：?????????????minminmax2)1(254)(LQCALLLCosESUNDi???對于Lsat5上試簡化為：????????????minminmax2255)(LQCALLLCosESUNDi??

7、?其中，QCAL為圖像灰度值DN。反照率的計算：TM1～TM4波段所對應的寬波段反照率可表示為個波段的反射率）第為iTMii???(41??TableTable1.1.acteristicsacteristicsofofthetheEnhancedEnhancedThematicThematicMapperMapperPlusPlus(ETM)(ETM)bs.bs.BBSpatialSpatialresolutionresolution

8、(m)(m)LowerLowerlimitlimit(m)(m)UpperUpperlimitlimit(m)(m)BwidthBwidth(nm)(nm)BitsBitsperperpixelpixelGainGainOffsetOffset128.500.450.527080.7862745216.1999998228.500.530.618080.8172548786.0000000328.500.630.696080.63960