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Remote Sensing Techniques

Remote sensing by imaging, as applied to Earth, goes back to the middle of the last century, when balloonists took the first photos. As applied to the rest of the solar system, we must look to the first observations (documented by sketches) made by Galileo in 1610, when he turned a telescope to the heavens and caught a glimpse of the surface complexities on our nearest neighbor, the Moon. Later, he confirmed the Copernican theories with his discoveries of moons, or orbiting satellites, around Jupiter. Since then, we have many observations of our solar system neighbors, first with telescopes and, after the opening of the Space Age, with orbiting spacecraft, flyby, probe, and lander missions. Most of the same instruments that survey the electromagnetic spectrum (EM) around Earth have been the principal tools for exploring our planetary associates and beyond¾ searching well into outer space at stars and other members of the Universe. Here is a list of remote sensing methods using EM spectral measurements that have provided exceptional information about planetary surfaces, atmospheres, and, indirectly, interiors: *

Gamma-Ray Spectroscopy
Gamma rays
Gamma spectrum K, U, Th Abundances Apollo 15, 16: Venera
X-ray Fluorescence spectrometry
Characteristic Wavelengths Surface mineral/ chemical comp. Apollo; Viking Landers
Ultraviolet Spectrometry
Spectrum of Reflected sunlight Atmospheric Composition: H,He,CO2 Mariner; Pioneer; voyager
UV, Visible
Albedo Nature of Surface; Composition Earth Telescopes; Pioneer
Multispectral Imagers
UV, Visible, IR
Spectral and Spatial Surface Features; Composition On most missions
Reflectance Spectrometers
Visible, IR
Spectral intensities of reflected solar radiation Surface Chemistry; mineralogy; processes Telescopes; Apollo
Laser Altimeter
Time delay between emitted and reflected pulses Surface Relief Apollo 15,16,17
Surface Polarization Surface Texture; Composition Pioneer; Voyager
Infrared Radiometer (includes scanners)
Thermal radiant intensities Surface and atmospheric temperatures; compos. Apollo; Mariner; Viking; Voyager
Microwave Radiometer
Passive microwave emission Atmosphere/Surface temperatures; structure Mariner; Pioneer Venus
Bistatic Radar
Surface reflection profiles Surface Heights; roughness Apollo 14,15,16; Viking
Imaging Radar
Reflections from swath Topography and roughness Magellan; Earth systems
Lunar Sounder
Multifrequency Doppler Shifts Surface Profiling and imaging; conductivity Apollo 17
S-Band Transponder
Doppler shift single frequency Gravity data Apollo
Radio Occultation
Frequency and intensity change Atmospheric density and pressure Flybys and Orbiters

* Adapted from Billy P. Glass, Introduction to Planetary Geology, 1982, Cambridge University, Press

This list is incomplete but is still highly representative. The Command and Service Module on the Apollo lunar missions carried a complement of other instruments including alpha-particle spectrometers, mass spectrometers, magnetometers, far UV spectrometers, scintillometers, and others designed to measure geochemical and geophysical properties. The astronauts also deployed, on the surface, instruments for specific studies. Among these were seismometers, magnetometers, gravimeters, solar wind gauges, cosmic-ray detectors, heat flow probes, and laser ranging retroreflectors. However, in retrospect, sensors that produce images, especially photographs and similar items, have provided the most direct and readily interpretible sets of data, and will continue to be a mainstay of future missions.


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Primary Author: Nicholas M. Short, Sr. email:

Collaborators: Code 935 NASA GSFC, GST, USAF Academy
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