Toward high-performance SPAD arrays for space-based atmosphere and ocean profiling LiDARs

Abstract

Space-based light detection and ranging (LiDAR) sensors have provided valuable insight into the global, vertical distribution of aerosol and cloud layers in Earth’s atmosphere, and, more recently, of the distribution of phytoplankton in the ocean. However, the photodetectors in these sensors lack the performance necessary to capture the vertical structure of cloud tops and ocean phytoplankton to a fidelity sufficient for advancing our understanding of the global water cycle and ocean carbon cycle, respectively. Recent advancements in high-performance single photon avalanche diode (SPAD) arrays promise to enable these measurements, while also offering a sensitivity that will allow significant reductions in laser power and telescope size, with associated sensor-level size, weight, and power (SWaP) savings. To harness the unique benefits of SPADs for these measurements, we propose to develop a large-format array of photon counting SPADs with <10 ns dead time, along with readout integrated circuitry that sums and bins (histograms) photon counts in real time to the desired temporal resolution for the target application. The feasibility of this approach has been investigated with a small-scale 8 × 8 SPAD array proof of concept hardware demonstration developed at Politecnico di Milano, with promising initial results. Progress is reported on designs that will allow scaling the array and readout integrated circuit electronics to the requisite of 128 × 128 size in a chip-scale, low power, photodetector ideal for LiDAR remote sensing of the atmosphere and ocean from SWaP-constrained platforms.