Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock ( ) or https://
means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
This study applied historical aerial imagery and satellite imagery to create digital surface models (DSMs) of the Helmand River Valley situated in southwestern Afghanistan. The historical imagery,...
data.gov
An official website of the GSA's Technology Transformation Services