Sensing and Interpretation Techniques

Whatever man’s ultimate goals in exploring the solar system may be, to satisfy curiosity, to locate additional habitats for the human race, or something else, achieving these objectives involves a common need. This is to map, in as much detail as possible, the morphology and constituents of the surfaces of all the planetary bodies and to determine the constituents and dynamics of the atmospheres of those bodies. For a variety of fairly obvious reasons, much of this information, a t least in the foreseeable future, will have to be obtained from safe (orbital) distances, i.e., by remote sensing. Although sensors of gravitational fields, magnetic fields, and possibly other phenomena may be important, this discussion will be confined to sensors of electromagnetic radiation in the ultraviolet, visible, and infrared ranges. Man has had centuries to map the surface and atmosphere of one body in the solar system, the earth. He has had access to practically all parts of the earth’s surface and recently has achieved the ability to place sensors and human observers in orbit about the earth. In spite of all this, there is much that is not known about the earth. How then can one seriously, in a generation or two, hope to make any appreciable headway in mapping hundreds of solar system bodies? Obviously, only by effecting some striking improvements in the tools and techniques for accomplishing the task. It is therefore disturbing to discover that improvements in the sensitivity and geometrical resolution of sensor instruments cannot provide the required increase in capability. Experience and calculation show that existing instrument techniques are adequate for even orbital use and capable of completely overloading present data interpretation capability. Furthermore, both resolution and sensitivity come close to physical limitations. Lenses and antennas operating near the Rayleigh limit are common. It is not so widely understood that presently achievable sensor sensitivities are, for the most part, also near theoretical limits. FIGURE 1 shows the sensitivities of many modern optical detectors as compared with the theoretical limit of detectivity. Many of these detectors come close to the theoretical limit of detectivity. It is well known that good modern radio frequency detectors are limited by fundamental physical processes. Therefore, not only are resolutions and sensitivities not presently limiting, but it does not appear likely that large improvements will be easily developed. It is the thesis of this paper that improvements of the type needed can be made by more sophisticated use of existing sensitivities and resolutions