The Electronically Steerable Flash Lidar: A NASA Facility Instrument for Ecological Studies

The Electronically Steerable Flash Lidar (ESFL) is a lidar concept created at Ball Aerospace and developed in conjunction with NASA. It represents a new paradigm for airborne or spaceborne lidar remote sensing. Instead of the mechanical scanning common to airborne lidars, or the fixed beam approach found in spaceborne lidars, ESFL allows the number and position of transmitted beams to vary shot-to-shot. This is done using an acousto-optic beam deflector that splits a single laser beam into N output beams, where N and the position of beam N on the ground can be reconfigured in real time electronically. This transmitter concept is coupled with a Flash Focal Plane Array (FFPA), a pixilated detector where every pixel delivers a time-resolved intensity waveform, thus allowing lidar imaging. The ESFL enables several jumps in capability for remote sensing of ecosystems. Multiple spatial scales can be probed simultaneously or within the same flight transect because beam spacings can be varied in real time. This means contiguous beams can be applied to regions where smaller scale variability needs to be probed, and in areas where maximum across-track coverage is needed, those beams are spread out. Furthermore, each beam can be projected onto multiple pixels, allowing one to collect a waveform over multiple length scales simultaneously. The electronic interface with the AOBD means that the transmitted pattern can respond to any of a multitude of inputs. The ESFL can interface with another forward-looking sensor, such as a hyperspectral instrument or another lidar or a digital camera. The data from that second sensor could be used to direct the ESFL observation toward, for example, an area with a specific spectral signature, or an area free from clouds. The ESFL concept was designed with a path to space in mind, but an airborne version has been built and tested on aircraft. The work continues under a NASA Airborne Instrument Technology Transition (AITT) grant designed to improve the reliability of the instrument. The AITT work will culminate in the ESFL becoming a NASA facility instrument, so that time on ESFL can be proposed through NASA. This allows public access to ESFL and ideally a long-term stream of data to the ecological community. The overall flexibility of the transmitter pattern and ability to alter it to respond to a changing scene makes the ESFL well-suited for many applications such as forest science, but also to track rivers for hydrological studies. This poster will discuss recent analysis of ESFL data in forests to prove its applicability to estimate canopy height in airborne systems. Furthermore, we will discuss improvements to the ESFL that are underway as part of the AITT to improve data throughput, allow for higher altitude operation, and increase overall reliability of the instrument.