REMS GTS: a pyrometer for Mars ground temperature measurement

Abstract

ABSTRACT This paper proposes a set of mathematical equations for modelling the REMS GTS, a pyrometer dedicated to measure the brightness temperature of the Martian surface. The equations complete a new simplified analytical thermal model based on an energy balance theory, which considers the inte rnal thermopile structure and operation, and the exchanged heat fluxes between detector transducer and the rest of the elements. The main advantage of this model, versus previous ones, is that it includes a direct relation between the sensor physical properties and the parameters of the model. Therefore, it is simple to establish a methodology to calibrate the system after a change or de gradation in any part of the sensor. In remote or hostile applications this property is very important and ne cessary. The model permits to establish a practical method to identify the model constants, and a differential in-flight calibration algorithm to determine and compensate the degradation of the sensor due to the depositi on of dust over the thermopile window. The main objective of this paper is to show, by using experimental data, the performance of the proposed model, analyzing its capability to measure the temperature of a target surface. It is also included a practical demons tration of the correct behaviour of the in-flight calibration algorithm. Keywords: IR temperature sensor; Sensor thermal model; Sensor calibration; Spacecraft instrumentation; Soil emissivity; Ground temperature; In-flight calibration; Dust deposition.