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地表温度是衡量地-气界面热状况的重要指标,在冻土制图、城市热岛效应等研究领域有重要应用.MODIS数据只提供了每日4次过境的瞬时温度值,而实际应用中往往需要日平均地表温度.对实测0cm温度数据进行分析后,发现其日变化曲线呈分段函数特性,白天按正弦曲线变化,夜间则呈线性下降.据此提出对白天和晚上的数据进行分段拟合的方案,并与已有的两种拟合方法作对比验证.地面验证工作包括两个方面:一是模拟的验证,按卫星过境时间从逐小时的实测0cm数据中挑出4个瞬时值,将上述拟合方法应用于这4个瞬时值,得到拟合的日平均温度,再同24h的算术平均值比较.结果表明:Sin-Linear法精度最高,平均误差在1K以内;其二是地面对MODIS的验证,将3种方法应用于MODIS数据,再与地面平均值比较,3种方法中Sin-Linear法误差最小,且具有最好的线性相关,R2超过0.9.
Surface temperature is an important index to measure the thermal status of geo-gas interface and has important applications in such fields as frozen soil mapping and urban heat island effect.MODIS data only provides the instantaneous temperature value of transit 4 times per day, which is often needed in practical applications Daily average surface temperature.Analysis of measured 0cm temperature data showed that the diurnal variation curve showed the characteristics of piecewise function, which was changed according to the sinusoidal curve during the daytime, and decreased linearly at nighttime.Accordingly, the daytime and nighttime data were subdivided The scheme is verified by comparison with the two existing fitting methods.The ground verification work consists of two aspects: one is simulation verification, which picks out four instantaneous values from the measured 0cm data by hour according to satellite transit time , The above fitting method was applied to these four instantaneous values to get the fitted daily mean temperature and then compared with the arithmetic mean value of 24h.The results showed that the precision of Sin-Linear method was the highest with the average error within 1K; secondly, MODIS validation of the ground, the three methods applied to the MODIS data, and then compared with the ground average, the three methods Sin-Linear least error, and has the best linear correlation, R2 exceeds 0.9.