Commercially manufactured complementary metal–oxide–semiconductor (CMOS) sensors have demonstrated competitive x-ray spectral imaging performance to the charge-coupled devices flown on the Suzaku and Chandra missions without the cooling demands required of these sensors. This performance, in combination with their reduced costs, warrants regarding CMOS sensors as promising candidates for low-Earth orbit (LEO) x-ray small satellites. We investigate the radiation tolerance of these devices to the anticipated total ionizing dose (TID) radiation expected in LEO. We expose a backside-illuminated Sony IMX290LLR CMOS sensor to up to 12 krad of TID from Cs137 gamma-ray radiation. We find an increase in the abundance of noisy pixels with increasing dosage, but no discernible increase in the average dark signal or RMS noise. Measurements of the x-ray spectrum from a Fe55 source indicate no change in spectral resolution and only minor gain degradation with TID.

<!-- *** Custom HTML *** --> Recently, complementary metal–oxide–semiconductor (CMOS) sensors have progressed to a point where they may offer improved performance in imaging x-ray detection compared to the charge-coupled devices often used in x-ray satellites. We demonstrate x-ray detection in the soft x-ray band (250 to 1700 eV) by a commercially available back-illuminated Sony IMX290LLR CMOS sensor using the Advanced Photon Source at Argonne National Laboratory. While operating the device at room temperature, we measure energy resolutions (full width at half maximum) of 48 eV at 250 eV and of 83 eV at 1700 eV, which are comparable to the performance of the “Chandra” ACIS and the “Suzaku” XIS. Furthermore, we demonstrate that the IMX290LLR can withstand radiation up to 17.1 krad, making it suitable for use on spacecraft in low Earth orbit.

The severity of wildfires is increasing and has driven increases in nighttime fire activity. Enhanced capability to detect the active burning regions of wildfires at night could significantly improve the effectiveness of wildfire management operations. Potassium line emission in the NIR near 770 nm is a signature of active burning. We test the use of multi-band imaging from an aircraft at night to distinguish a wood-burning fire from artificial light sources. We find that a simple ratio of the signals in two broad bands, one including 770 nm, effectively discriminates the fire from artificial light sources. This offers the possibility of nighttime fire detection with high spatial resolution using silicon sensors sensitive in the NIR.

The demonstrated performance and cost-effectiveness of complementary metal–oxide–semiconductor (CMOS) sensors make them a potentially attractive option for low-cost space-based X-ray observatories. We have previously reported on the performance of a commercially available backside-illuminated Sony IMX290LLR-C CMOS sensor and found it to offer X-ray spectral resolutions comparable to the charged coupled devices (CCDs) aboard Suzaku and Chandra and to have a sufficient radiation hardness for use in low Earth orbit. In this work, we report on the quantum efficiency (QE) of this sensor, an essential metric for modeling the sensitivity of an instrument as an X-ray detector. Using the Advanced Photon Source at Argonne National Laboratory, we measure the soft X-ray QE of this CMOS sensor to be 0.28±0.02 at a photon energy of 490.5 eV. This energy was chosen for its proximity to the astrophysically important O VII triplet emission lines (∼574 eV) studied by the HaloSat mission. Although not surpassing that of the back-illuminated CCDs aboard Suzaku and Chandra, this QE compares favorably to that of the front-illuminated CCDs aboard the same observatories and is competitive with that of the silicon drift detectors used aboard HaloSat, making it a strong candidate for use on future X-ray small satellite (SmallSat) missions.

We present a low-cost prototype of a visible and near-infrared (VIS-NIR) remote sensing platform, optimized to detect and characterize natural flaming fire fronts from airborne nighttime light (NTL) observations, and its radiometric calibration. It uses commercially available CMOS sensor cameras and filters with roughly 100 nm bandwidths to effectively discriminate burning biomass from other sources of NTL, a critical ability for wildfire monitoring near populated areas. Our filter choice takes advantage of the strong potassium line emission near 770 nm present in natural flaming. The calibrated cameras operate at 20 ms of exposure time and boast radiance measurements with a sensitivity floor, depending on the filter, in the range 3–5 $\times {10}^{-6}$ W m⁻² sr⁻¹ nm⁻¹ with uncertainties lower than 5% and dynamic ranges near 3000–4000. An additional exposure time with a tenth of the duration is calibrated and extends the dynamic range by a factor of 10. We show images of a spatially resolved fire front from an airborne observation of flaming biomass within this radiance range.