宽波段发射率对长波净辐射估算影响分析

Influence of the optimal broadband emissivity spectral range on calculating surface longwave net radiation

地表宽波段发射率是估算地表长波净辐射的关键参数。陆面模式计算的是4～100μm的地表长波净辐射,而遥感仅能提供3～14μm范围内的宽波段发射率。评价遥感宽波段发射率用于地表长波净辐射计算的精度,需要光谱范围更宽的地表发射率光谱。借助辐射传输模型模拟的水体、冰/雪和矿物1～200μm发射率光谱,调查了不同光谱范围的宽波段发射率和全波长宽波段发射率的差异。结果表明4～100μm宽波段发射率与全波长宽波段发射率最接近。调查了不同光谱范围内遥感宽波段发射率在计算4～100μm长波净辐射的精度,发现8～13.5μm的宽波段发射率具有最高的精度,偏差小于0.01W/m2,均方根误差小于1W/m2。并给出由ASTER和MODIS窄波段发射率产品计算8～13.5μm宽波段发射率的转换公式。

Surface broadband emissivity （BBE） in thermal infrared is an important parameter for estimating the net surface longwave radiation. The BBE at 4 - 100μm is needed in land surface models. However, the BBE estimated from remote sensing narrowband emissivity product is limited to 3 -14μm. More realistic emissivity spectra are essential to evaluate BBE at which spectral domain could be used to calculate net surface longwave radiation in land surface models. By virtue of modem radiative transfer tools, the emissivity spectra of water, snow and minerals in approximately 1 - 200μm were derived. With these emissivity spectra, we investigated the difference of BBE at all wavelength and those at different spectral domains and found that BBE at 4 - 100μm can replace BBE at all wavelength. We also examined the accuracy of BBE that could be calculated from remotely sensed narrowband emissivity products in estimating the net surface longwave radiation. The BBE at 8 - 13.5μm could be used to calculate the net surface longwave radiation in land surface models with a bias of 0.01W/m2 and a RMS less than 1W/m2. Using more representative emissivity spectra, we derived the conversion coefficients of the linear functions that can be used to calculate BBE at 8 - 13. 5 μm from ASTER and MODIS narrowband emissivity products.