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一般在分析陆地卫星的影像数据时,是利用记录在计算机兼容磁带上的每个象元的数字来实现的,虽然,对于单一象元来说,这一方法是令人满意的;但是,如果在分析或使用多象元来作镶嵌或多次重叠使用时,则这一方法可能产生错误的结果。应该将每个象元值转换成它们相应的具有等效物理量纲的数值(即具有物理意义的数字)。例如(1)辐射强度,即在卫星轨道上测到的辐射能量,量纲为每(立体)弧度,每平方厘米的毫瓦数值(mWcm~(-2))或(2)反射率。这些数值的变化取决于:依据每颗卫星在一定的时间、太阳高度角、大气状态、地形走向和坡度、以及地面覆盖类型等,对多波段扫描仪的核准。大气的核准必不可少,但是,已超出本文的目的和范围。对于陆地卫星1、2和3号的目前五个波段是在忽略大气校正的情况下,用给定的方程计算辐射强度值和反射率的。本文的一个例子中,可以看出不同的卫星计算出的辐射强度和反射率有很大的不同。在分析陆地卫星资料时,把陆地卫星数据表达为天然辐射值,将减少错误。
The analysis of terrestrial satellite image data is generally performed using the number of each pixel recorded on the computer compatible tape, although this method is satisfactory for a single pixel; however, if This method can produce erroneous results when parsing or using multiple pixels for mosaic or multiple overlays. Each pixel value should be converted into their corresponding numeric value with equivalent physical dimensions (ie, a number that has a physical meaning). For example: (1) Radiation Intensity, which is the radiant energy measured in the orbit of a satellite, in the order of milliwatts per square centimeter (mWcm -2) or (2) reflectivity. These values vary depending on the approval of the multi-band scanner based on the time of each satellite, the solar elevation angle, the state of the atmosphere, the direction and slope of the terrain, and the type of ground cover. Atmospheric approval is essential, however, beyond the purpose and scope of this article. For the current five bands of Landsat 1, 2 and 3, the radiation intensity values and reflectivities are calculated using the given equations, ignoring the atmospheric correction. In an example of this article, it can be seen that radars and reflectivities calculated by different satellites are quite different. Expressing terrestrial satellite data as natural radiation in the analysis of terrestrial satellite data will reduce errors.