Sizing Chemical Flow Rates for Infrared Imaging Spectrometers
Abstract
For many years now, the Imaging Spectroscopy Department has been releasing chemicals into the atmosphere at accurately measured rates, producing chemical plumes for infrared hyperspectral imaging spectrometers. The purpose is often to determine how well such a spectrometer and its software can identify the chemicals in the plume and determine the rate at which each chemical is being released. We are often asked to release a chemical at a rate that is barely detectable or at some multiple of that rate. The minimum detectable release rate does not have a fixed value; rather it varies with background temperature, wind speed, and air temperature, all of which we measure before every release. For an infrared imaging spectrometer viewing a plume from the ground against the sky, the background temperature is the sky radiometric temperature; when airborne and viewing ground, the background temperature is the ground radiometric temperature. In this report, a simple, approximate equation is derived that shows how the expected minimum detectable release rate (or some multiple of it) varies with ground radiometric temperature, wind speed, air temperature, and the ground sampling distance (which depends on the field of view of the spectrometer and its distance from the plume). This equation can be easily adapted to the situations in which the background is the sky, or trees, or any other object.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 21, 2016
- Accession Number
- AD1159925
Entities
People
- Karl Westberg
Organizations
- The Aerospace Corporation