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Instructions for Downloading and Using SRTM Data with the Pathloss program.

SRTM data are distributed in two levels: SRTM-1 with data sampled at one arc-second intervals in latitude and longitude (USA only), and SRTM-3 sampled at three arc-seconds. Three arc-second data are generated by three by three averaging of the one arc-second samples.

Data are divided into one by one degree latitude and longitude tiles in "geographic" projection, which is to say a raster presentation in no projection at all but easy to manipulate and mosaic.

File names refer to the latitude and longitude of the lower left corner of the tile - e.g. N37W105 has its lower left corner at 37 degrees north latitude and 105 degrees west longitude. To be more exact, these coordinates refer to the geometric center of the lower left pixel, which in the case of SRTM-3 data will be about 90 meters in extent.

The data can be downloaded at ftp://e0srp01u.ecs.nasa.gov/srtm. These files are compressed using pkzip. You will need to unzip the files before they can be used.

How to use the SRTM data with the Pathloss program.

The SRTM data uses the WGS84. NAD83 and NAD27 Coordinates are transformed automatically.

In the Pathloss program click "Configure" – "Terrain Database" and select "SRTM" from the drop down list. Click Setup Primary (or Secondary depending on your selection). Click the file button and browse to find and load a file with the HGT extension. The program is now setup to use the selected SRTM file.