Digital Geography

Adding projection data to ENVI headers (GIMMS 3g example)

Once in a while you may need to take an unprojected file and add coordinate parameters to the header. Assuming you use ENVI, the hard way is to perform a reprojection via Image to Map registration in ENVI Classic. The easy way is to add the coordinate information to the header file. Here we assume you do not need to warp the file to an ellipsoid or datum. Here we use the example of GIMMS 3g data from the University of Maryland and NASA. Start by importing the data as a Binary file.   It is important to realize that…

Remote Sensing at AGU (part II- vegetation time series)

In a previous post I talked about some of the remote sensing themes during the first half of the American Geophysical Union Fall meeting. Here I want to talk about the latter part of the week at AGU and the headline remote sensing topic: vegetation time series. In the early 1970s Compton J. Tucker investigated the spectral reflectance of prarie grass, leading to a host of publications in the mid to late 1970s on spectral reflectance of vegetation, the use of multispectral satellite imagery for vegetation monitoring and, ultimately, the Normalized Difference Vegetation Index (NDVI). At AGU we saw that NDVI…

short announcement: Earth Engine by Google

On the 9th of May Google introduced an astonishing new technology that makes the good old flickr function in Erdas Imagine quite useless. With the Earth Engine from Google Earth you will be able to see the world change since 1984. They have compiled about 900 terabyte of Landsat Data. So they stitched, balanced the contrast, analysed and ordered about 2’000’000 images of the world to provide a comprehensive look into Earth’ history: Erdenet (Mongolia): coal mining lake Ugii Nuur (Mongolia): drying and dying Jänschwalde (Germany): coal mining Las Vegas (USA): urban sprawl Additionally you are able to browse the…

NDVI / SAVI calculation using Landsat scenes: DNs vs reflectance values

In one of my last seminars relating remote sensing techniques I was blamed for calculationg the NDVI and SAVI directly with the ModelMaker in Erdas Imagine using digital numbers (so-called DNs) instead of reflectance values. So I analyzed the influence of using DNs instead of reflectances. You can see some little thoughts and results on that here…