干旱区生态环境知识资源中心

We have developed a miniature range-gated step-frequency (RGSF) ground penetrating radar (GPR) for use in mapping subsurface structures from planetary rovers such as the rover associated with the Mars 2009 Smart Lander Mission. At each stepped frequency the antenna is used to both transmit and receive RF radiation. Radiation scattered back from the subsurface is amplified, mixed with a frequency reference, detected as an in-phase amplitude, and transformed from the frequency domain to the time/distance domain for interpretation. When fully developed, the frequency range will be from approximately 10 MHz to 500 MHz. Compared to conventional impulse GPRs, the RGSF system has a similar total operational bandwidth, but at any instant of operation, the transmitter/receiver system is tuned to a narrowband configuration. It can provide high average transmitter power per frequency and allow low sampling rate. This capability provides both significantly enhanced depth penetration and delineation of fine-scale interfaces. Our prototype GPR has miniaturized radar electronics (3 x 12 x 3 cm, 3W power, 30g), with a battery (14 V, 760 g) and a resistively loaded dipole antenna (2.3 m length, currently operating from 30 MHz - 150 MHz). Field testing of the prototype has been conducted over alluvium and a basaltic lava flow near the Lunar Crater Volcanic Field, Nevada, along a breakout channel north of the Silver Lake Playa, Mojave Desert, California, and over till and ash on Mauna Kea, Hawaii. Comparisons to known subsurface structures for the test sites demonstrate that the system is capable of resolving fine-scale variation in lava flow thickness, the depth to bedrock beneath the aeolian fill and alluvium in the break-out channel, and variations in till and ash thickness, from depths from meters to approximately 10 meters.