A programmable riometer for Earth and Mars

We have developed a miniature radio receiver designed to operate as a relat ive ionospheric opacity meter (riometer). This project was funded by NASA a s an enabling technology for future planetary radio science missions. We so ught to reduce the instrument's size, mass, and power so that it would be p ractical for a Mars lander or rover mission. A recent study by our group in dicates that a riometer might work well on Mars and offers a potentially ri ch science return. The technology also has immediate terrestrial applicatio ns. For example, the University of Maryland operates a chain of imaging rio meters at the Automatic Geophysical Observatories (AGOs) in Antarctica. Our riometer includes features that are desirable for extended autonomous oper ation such as those with AGOs: low power consumption, wide dynamic range an d linearity, computer command and data interface, and the ability to be rem otely reconfigured. The receiver design provides significant improvements o ver previous implementations used in riometers. The high degree of system l inearity, combined with a digital feedback loop (including a low-duty calib ration cycle), allows more time for viewing the radio sky. We implemented s everal of the receiver subsystems in a field-programmable gate array, inclu ding the receiver detector, the control logic, and the data acquisition and processing blocks. Considerable efforts were made to eliminate or minimize RF noise and spurious emissions generated by the receiver's digital circui try. Results of laboratory and field tests are presented and discussed.