基于多源遥感数据的(HJ-1A/B和MODIS数据)30米空间分辨率日地表反照率的反演方法研究

Land surface albedo based on remote sensing data is the most efficient way to monitor global and regional climate, ecosystems and land surface energy balance. Many scientific studies on urban environments have been conducted in recent years, such as those on urban heat islands and urban land surface energy balance, which require land surface albedo data with a high spatio-temporal resolution. To address this problem, we expand our previously described method for deriving land surface albedo with a 2–4-day temporal resolution and a 30-m spatial resolution to derive daily land surface albedo at a 30-m spatial resolution. The proposed method works by combining the downscaled daily land surface reflectance data at a 30-m spatial resolution with the Moderate Resolution Imaging Spectroradiometer (MODIS) land surface bidirectional reflectance distribution function (BRDF) parameters product (MCD43A1), which has a spatial resolution of 500 m and a temporal resolution of 8 days. Firstly, downscaling daily MODIS land surface reflectance data (MOD09GA) from 500 m to 30 m on the basis of land surface BRDF parameters for HJ-1A/B with a spatio-temporal resolution of 30 m and 2–4 days is performed; this is the key step in the improved method. Subsequently, the daily land surface BRDF parameters at the 30-m spatial resolution are calculated on the basis of a priori knowledge from the MODIS BRDF product and the downscaled daily land surface reflectance at 30 m. Finally, the calculated high-resolution BRDF parameters are integrated over the illuminating/viewing hemisphere to produce the daily land surface albedo at the 30-m resolution weighted by downwelling solar radiation arriving at the ground.

遥感数据驱动的地表反照率参数有效地实现了全球/区域尺度上的气候变化监测及地表能量平衡监测。随着社会经济的发展，对应的问题如城市热岛效应、城市净辐射的变化引发的社会环境问题都需要有更高时空分辨率的地表反照率产品来支持这些问题的研究。在博士研究生阶段的工作中，我们已经成功地利用HJ-1A/B地表反射率数据与MODIS BRDF参数驱动了30米的2～4天的地表反照率参数；本研究在前期工作的基础上，我们进一步引入MODIS地表反射率数据及HJ-1A/B BRDF参数，并将引入的数据与HJ-1A/B地表反射率数据进行融合降尺度获得30米的日地表反射率数据，并基于一个经验的方法将降尺度的地表反射率数据与MODIS BRDF参数结合驱动30米的日地表反照率参数。

当前的地表反照率产品的时空间分辨率对于小尺度区域的高频率变化研究具有重要意义，注入监测城市热岛以及城市能量平衡等问题。我们当前的地表反照率产品具有2-4天、30米的时空分辨率，虽然该时空特性已经是当前最高的，但是仍然不能满足这种小尺度、高频率的观测。降尺度的方法给我们提供了这个机会来进一步提升地表反照率的时空分辨率。我们的研究中介绍了一个方法通过降尺度地表反射率来驱动地表反照率参数。具体地，我们利用了MODIS 500米地表反射率数据降尺度到30米，然后一个30米每天的地表反射率结合HJ-1A/B BRDF经验知识库可以被获得。