我正在处理对流层的NO2柱密度,我的数据源是TEMIS。
NO2 level3数据可以从OMI仪器的原始信息中得到。
我下载了两类数据,。Grd 和。Kml 为同月。
我在谷歌Earth中打开它,图如下:
可以看到NO2 trop的数据范围。列为0~20,与网站上的模板图相同。
我没有找到关于这个数据的详细信息。其中-999
为no_data place。
我使用python读取并绘制空间分布。
filename = './CH2O-NO2/no2_201306.grd' def read_grd(filename): ncols = np.array(linecache.getline(filename, 1)[6:10]).astype(float) nrows = np.array(linecache.getline(filename, 2)[6:10]).astype(float) xllcorner = np.array(linecache.getline(filename, 3)[10:14]).astype(float) yllcorner = np.array(linecache.getline(filename, 4)[10:14]).astype(float) cellsize = np.array(linecache.getline(filename, 5)[9:14]).astype(float) nan_value = np.array(linecache.getline(filename, 6)[13:17]).astype(float) longitude = xllcorner + cellsize * np.arange(ncols) latitude = yllcorner + cellsize * np.arange(nrows) value = np.loadtxt(filename, skiprows=7) value = value[::-1] return value, longitude, latitude, nan_value no2,lon_no2, lat_no2, nan_value = read_grd(filename) no2[no2 == nan_value] = np.nan def isnt_NaN(num): return num == num no2[isnt_NaN(no2)].max() > 9999.0
It seems that the high value in grd format data are out of the regular condition which can be learned from previous resarch (Hot spots of NO2 column are about 15~20 10^15 molec/cm2).
Does anyone familiar with the OMI-NO2 data? I don't know how to deal with the irregular value which are way too higher than realistic.
似乎您担心数据中的值超过kml文件中显示的颜色条上的最大值。我不担心这个。您使用的是月平均“3级”产品,根据定义,这是高度质量控制的产品。对于全球大多数地区,典型的数值将在1 x 10^14和5 x 10^15摩尔/平方厘米之间变化。超过20 x 10^15 molec/cm2的值只出现在高度污染的地区。OMI NO2产品中非常大的值是现实的,特别是在东南亚,那里获得了最大的NO2柱。我有时甚至看到值超过1 x 10^17。当信号变大时,检索的可信度就会提高。实际上,应该谨慎对待的是较低的值(例如小于8 x 10^14 mol /cm2),因为任何低于这个值的值都可能是“噪音”。为了显示全球范围内值的方差(可以跨越4个数量级),选择的颜色刻度效果很好。 Note that the color bar is a logarithmic scale, which helps give definition to the plots in the regions with typical values. You could rewrite the kml file though, and pick a different max value, if you are interested in better plots of southeast Asia.
If you are interested in learning more about the product, I highly suggest you see Boersma (2011) and also refer to the user manual.