DEVELOPMENT OF A HIGH PRECISION THERMAL INFRARED FIELD 
RADIOMETER 
C. PIETRAS*, N. ABUHASSAN** M. HAEFFELIN*, G. BROGNIEZ*, M. LEGRAND*, J.-P. BUIS*** 
*Laboratoire d’Optique Atmosphérique, Université des Sciences et Technologies de Lille, 
59655 Villeneuve d’Ascq (France) 
** Centre CNRS de Recherche Géophysique, 58150 Garchy, (France) 
*** Société CIMEL, 5 Cité Phalsbourg, 75011 Paris (France) 
ABSTRACT 
A multichannel radiometer, which is designed to have up to six channels, with the capability of operating in 
various spectral domains of the thermal infrared -in particular the atmospheric windows at 3.7 and 10 pm- is 
presented. The detector is a fast thermopile characterized by a very low temperature dependence of the 
responsivity. Instrument operation and measurement storage are managed by a processor. In addition to 
instrument automatization, this managing system allows the time range in field work to be increased by 
optimizing the energy consumption. Self-calibration of the radiometer is performed by an internal blackbody. 
The optics and electronics of the instrument are presented along with the basic performances: 
precision, sensitivity, spectral characteristics, and time constant. The preliminary studies of the instrument 
characteristics were performed on a wide field-of-view bread board. Sensitivity, noise and instrument 
calibration were performed on a four channel wide field-of-view prototype. 
The objectives of this instrument, which is designed to be aircraft- and balloon- bomed, are to perform 
measurements of ground and vegetation, on the one hand, and clear sky and cloud radiances, on the other hand. 
Calibrations and analyses of satellite radiometric data is a major field among expected applications. 
KEY WORDS : Radiometer, Thermal Infrared, Remote Sensing. 
1 - INTRODUCTION 
In treating research topics concerning ice crystal clouds [1] and atmospheric aerosols [2] at the Laboratoire 
dOptique Atmosphérique, the availability of accurate and reliable multispectral measurements in the thermal 
infrared appears to be more and more crucial. These needs are related to, on the one hand, intensive ground 
and airborne measurement campaigns, and on the other hand, routine measurements collected over long 
periods of time. Concurrently to these objectives, surface remote sensing applied to temperature and surface 
emissivity determination as well as to the study and monitoring of vegetation are current concerns in the field 
of remote sensing and agronomy [3]. If these various measurements are interesting as such, their purpose is 
essentially to control, analyze and validate satellite measurements. 2 
2 - REQUIRED CHARACTERISTICS 
A number of specifications are required when considering all possible applications. 
(i) A version with narrow field of view (3° for cloud observation) and a version with wide field of view (10° 
for surface monitoring) are under study. 
(ii) Up to six channels between 3.5 and 15 pm allow multispectral measurements to be performed such as 
surface signature, analysis of atmospheric components, utilization of satellite IR channels. 
(iii) The instrument must be able to measure apparent radiative temperatures in a range between - 100°C and + 
100°C. The precision of the measurement must be 0.05°C for a 1-second integration time (with possibility of 
a 0.1-second integration time) and a 1 -pm wide spectral interval in the 8-14 pm window. 
(iv) For field measurement applications as well as for network utilization, the instrument must be: 
- portable (up to 5 kg), 
- self-contained (one-day time range with batteries or unlimited time range with solar panels), 
- automatic with a motorized support, 
(v) The instrument must be able to endure various and severe weather conditions (rain, dust, frost, heat, 
humidity, corrosion): 
- ambient temperature conditions: -20°C to +50°C, 
- surrounding humidity: 0 to 100 %, 
- protection against dust and rain for the crucial elements. 
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