Design and fabrication of net flux radiometers for Mars exploration

Abstract

We report on the development of a net flux radiometer as part of a wireless sensor network for the acquisition of surface meteorological data on Mars. The radiometer makes use of four separate sensors to measure simultaneously: (i) global solar radiation; (ii) ground reflected solar radiation; (iii) sky emitted infrared radiation; and (iv) ground emitted infrared radiation. To perform measurements in the broad spectral range from 0.2 to 50 μm, goldblack coated microbolometers of 100 um size were fabricated for use in custom packaged pyranometers and pyrgeometers. Each microbolometer was placed at the center of an optically coated dome which provided a field-of-view of 180° and acted as a bandpass filter. Under nominal operating conditions the microbolometer showed a responsivity of ~ 75 kV/W and a time constant of ~ 13 ms. Parametric characterization of the radiometer provided a set of bias voltages, integration time, and temperature set points that help prevent the issue of output saturation in field operation conditions. The measured sensitivity, in the range from 2 to 6 mV/(W/m2), and measured resolution, from 0.06 to 0.15 W/m2, compared favorably with those of commercial net flux instruments. The results obtained in the field operation confirmed that the temporal responses of the pyranometer and pyrgeometer are in good agreement with the responses of the commercial instrument. However, a signal drift was observed, mostly in the pyrgeometer data, over a long period acquisition. This drift, which appears to be in correlation with changes in the environment temperature, is believed to be a result of the dome heating effect.