Lidar echo emulator – Near-infrared, visible, and ultraviolet

Abstract

A compact and cost-effective NIR-VIS-UV lidar echo emulator (LEE) was designed and manufactured as a compact breadboard. The LEE is an application-specific optical pulse shaper delivering a short lidar return (echo) in the ns range overlapped with an extended lidar return in the µs range with a repetition rate from 100 Hz – 500 Hz. The short echo power levels range from 0.2–200 nW, whereas the long echo powers from 0.1–25 pW. The coarse power tuning between the two echoes is done using variable attenuators. LEE provides three operation modes: short echo, long echo, or both echoes overlapped. The power difference between the echoes exceeds 60 dB in the overlapping mode.

Introduction

Lidar is an active remote sensing technique that has become essential for atmospheric and land surface remote sensing. In the last two decades, lidar systems have been part of numerous space missions such as CALIPSO (NASA, 2006) or ADM Aeolus (ESA, 2018). Nowadays, one of the space missions’ main challenges is implementing a complex lidar instrument on a small satellite platform with limited resources. The limiting factors are the telescope size and detector size; therefore, the receiver and detector noise are critical parameters. The detector and the following amplifier stages must be as noiseless as possible. HgCdTe (MCT) avalanche photodiode (APD) detectors are currently the promising candidates due to their exceptional performance in terms of high linear gain, low excess noise, high quantum efficiency, and low dark current at low temperatures. However, even the MCT APD detector must be optimized to address the most challenging lidar applications like the forthcoming MERLIN-ESA mission.