A sensor device configured to measure a level of carbon dioxide in a body of gas, the sensor device comprising: a radiation source configured to emit electromagnetic radiation through the body of gas; a sensor comprising (i) a first lead selenide detector arranged such that electromagnetic radiation emitted by the radiation source that has passed through the body of gas becomes incident on the first lead selenide detector and (ii) a second lead selenide detector arranged to receive a portion of the electromagnetic radiation emitted by the radiation source after the electromagnetic radiation has passed through the body of gas, the sensor being configured to generate (i) a first signal conveying information related to the intensity of electromagnetic radiation incident on the first lead selenide detector and (ii) a second signal conveying information related to the intensity of electromagnetic radiation incident on the second lead selenide detector; a first thermal sensor that is discrete from the first lead selenide detector, wherein said first thermal sensor is configured to output a first temperature signal conveying information related to a temperature of said first lead selenide detector; a processor configured to determine a level of carbon dioxide in the body of gas based on the first and second signals generated by the sensor; and characterized in that the sensor device further includes: a second thermal sensor that is discrete from the second lead selenide detector, wherein said second thermal sensor is configured to output a second temperature signal conveying information related to a temperature of said second lead selenide detector; wherein the processor is further configured such that determination of the level of carbon dioxide involves a compensation for the temperatures of the first and the second lead selenide detector (32, 34) as reflected in the first and the second temperature signal. a radiation source configured to emit electromagnetic radiation through the body of gas; a sensor comprising (i) a first lead selenide detector arranged such that electromagnetic radiation emitted by the radiation source that has passed through the body of gas becomes incident on the first lead selenide detector and (ii) a second lead selenide detector arranged to receive a portion of the electromagnetic radiation emitted by the radiation source after the electromagnetic radiation has passed through the body of gas, the sensor being configured to generate (i) a first signal conveying information related to the intensity of electromagnetic radiation incident on the first lead selenide detector and (ii) a second signal conveying information related to the intensity of electromagnetic radiation incident on the second lead selenide detector; a first thermal sensor that is discrete from the first lead selenide detector, wherein said first thermal sensor is configured to output a first temperature signal conveying information related to a temperature of said first lead selenide detector; a processor configured to determine a level of carbon dioxide in the body of gas based on the first and second signals generated by the sensor; and characterized in that the sensor device further includes: a second thermal sensor that is discrete from the second lead selenide detector, wherein said second thermal sensor is configured to output a second temperature signal conveying information related to a temperature of said second lead selenide detector; wherein the processor is further configured such that determination of the level of carbon dioxide involves a compensation for the temperatures of the first and the second lead selenide detector (32, 34) as reflected in the first and the second temperature signal. a second thermal sensor that is discrete from the second lead selenide detector, wherein said second thermal sensor is configured to output a second temperature signal conveying information related to a temperature of said second lead selenide detector; wherein the processor is further configured such that determination of the level of carbon dioxide involves a compensation for the temperatures of the first and the second lead selenide detector (32, 34) as reflected in the first and the second temperature signal.