Europe puts into orbit two Earth observation satellites

Earth observation satellites currently struggle to see through dense or dark environments such as the night ocean or dense forests due to a lack of photons. Standard optical sensors require abundant light, which is scarce in these regions, limiting their ability to capture useful data. Researchers Dr. Sumanta Das and Dr. Malini Roy Choudhury from Ramakrishna Mission Vivekananda Educational and Research Institute propose a solution using quantum photonics.

They have developed a new approach called quantum-enhanced multispectral remote sensing (QEMRS) that can retrieve high-quality information using fewer photons than conventional cameras. QEMRS operates through two modes: passive and active. In passive mode, it captures faint natural light reflecting from Earth using superconducting nanowire single-photon detectors that are ultra-sensitive and operate at cryogenic temperatures.

In active mode, the satellite generates a pair of entangled photons, beams one down to Earth to interrogate a target, and measures the correlated signal to identify the target even through overwhelming background noise. However, implementing QEMRS in space faces challenges such as atmospheric distortion, large cooling systems, and high power consumption.

The researchers suggest a dual-layer calibration strategy to ensure the data remains scientifically useful, using simulated dark environments and faint earthshine from the moon for calibration. QEMRS is seen as a complementary sensing modality, enabling observations in photon-limited environments and opening a new domain for Earth and planetary science.