New Generation Bolometric Detector for Measurement of Solar Spectral Irradiance

We have developed a novel room temperature vertically aligned carbon nanotube (VACNT) bolometer for the Compact Spectral Irradiance Monitor (CSIM), a miniaturized space­based solar spectral radiometer. This 6U CubeSat instrument will measure the solar spectral irradiance from 200­-2400 nm; a continuous spectral range that covers 96% of the total solar output. The on-orbit radiometric stability of the CSIM instrument must meet or exceed 100 ppm/year in order to generate a data record useful for climate modeling over a solar cycle. For CSIM, both radiometric accuracy and long­term stability are provided by this absolute electrical substitution bolometer. Due to its basic thermal operation the bolometer has a very flat spectral response and is robust to degradation on orbit. The bolometer is based on a micro-machined silicon substrate with a silicon nitride thermal link utilizing highly developed processing techniques. The measured noise level for the bolometer is 260 pW for a 40 second measurement, demonstrating over a factor of four improvement compared to the presently used space-based designs. More generally, the development of these bolometers integrated into ambient-temperature radiometers offer unique opportunities to acquire more frequent Earth radiation balance measurements by providing miniature, low-power absolute detectors for SmallSat implementation.