Remote Sensing Through Millimeter Wave Radiometer Sensor

Abstract

The extension of imaging techniques from shorter wave length of IR and visible to longer wave length of mm
wave invites substantial penalties to be paid in terms of size and spatial resolution. In spite of the above cited
limitations, passive imaging sensors have gained popularity due to its superior performance under adverse
weather conditions i.e. fog, dust &battle field smoke. Besides operating under stealth conditions the images
generated have a high contrast, stable signature and provide easy interpretation of images. Millimeter wave
imaging through passive radiometric sensor is proving to be a great boon for the covert surveillance of
battlefield by sensing the manmade objects, and armored vehicles from a remote platform. The all-weather
capability of mm wave imaging sensor provides the necessary edge over the other technologies as part of sensor
suit for imaging. Passive mm wave imaging system develops a picture by detecting non-coherent noise i.e.
Radiant electromagnetic energy. In this band, emissivity varies greatly from near zero for metallic objects to
nearly one for natural objects like vegetation. Metallic objects appear very cold to a passive MM wave sensor
due to their low emissivity (high reflectivity) relative to terrain and other non-metallic objects in the image.
Because, these metallic objects are almost totally reflective, so any type of counter measure will have little
effect on their detection. The key to passive MM wave imaging is the large temperature contrast in the MM
wave spectral band due to large variation in emissivity value for the various target materials and terrain in an
imaged scene. Temperature contrast of greater than 100 times the contrast of IR systems are common for the
systems operating in the MM wave spectral band as any material at a temperature above absolute zero radiates
in microwave, Millimeter wave and other spectral regions. All objects in a given scene of interest are either
reflecting or radiating electromagnetic energy in a given spectral band. Present paper discusses the usage of
94GHz imaging sensors with single receiving elements for the purpose of surveillance, its detection capabilities
and image data of the metallic targets in the background of ocean, land and hilly terrain