Algorithm for Detection of Ground and Canopy Cover in Micropulse Photon-Counting Lidar Altimeter Data in Preparation for the ICESat-2 Mission

Abstract

Abstract. The Ice, Cloud and Land Elevation Satellite-II (ICESat-2) mission has been selected by NASA as a Decadal Survey mission, to be launched in 2016. Mission objectives are to measure land ice elevation, sea ice freeboard/ thickness and changes in these variables and to collect measurements over vegetation that will facilitate determination of canopy height, with an accuracy that will allow prediction of future environmental changes and estimation of sea-level rise. The importance of the ICESat-2 project in estimation of biomass and carbon levels has increased substantially, following the recent cancellation of all other planned NASA missions with vegetation-surveying lidars.Two innovative components will characterize the ICESat-2 lidar: (1) Collection of elevation data by a multi-beam system and (2) application of micropulse lidar (photon counting) technology. A micropulse photon-counting altimeter yields clouds of discrete points, which result from returns of individual photons, and hence new data analysis techniques are required for elevation determination and association of returned points to reflectors of interest including canopy and ground in forested areas.The objective of this paper is to derive and validate an algorithm that allows detection of ground under dense canopy and identification of ground and canopy levels in simulated ICESat-2-type data. Data are based on airborne observations with a SigmaSpace micropulse lidar and vary with respect to signal strength, noise levels, photon sampling options and other properties. A mathematical algorithm is developed, using spatial statistical and discrete mathematical concepts, including radial basis functions, density measures, geometrical anisotropy, eigenvectors and geostatistical classification parameters and hyperparameters. Validation shows that the algorithm works very well and that ground and canopy elevation, and hence canopy height, can be expected to be observable with a high accuracy during the ICESat-2 mission. A result relevant for instrument design is that even the two weaker beam classes considered can be expected to yield useful results for vegetation measurements (93.01-99.57% correctly selected points for a beam with expected return of 0.93 mean signals per shot (msp9) and 72.85% -98.68% for 0.48 msp (msp4)). Resampling options affect 1 https://ntrs.nasa.gov/search.jsp?R=20120012964 2019-06-20T00:45:47+00:00Z results more than noise levels. The algorithm derived here is generally applicable for analysis of micropulse lidar altimeter data collected over forested areas as well as other surfaces, including land ice, sea ice and land surfaces. (1) IntroductionDetermination of vegetation height of the Earth's forests is an essential requirement in estimation of global and regional biomass and carbon levels. Because of the scale of the problem and the inaccessibility of many of the Earth's forested areas, this is best achieved from satellite. NASA's Ice, Cloud and Land Elevation Satellite (ICESat) mission (2003)(2004)(2005)(2006)(2007)(2008)...

Combining satellite lidar, airborne lidar, and ground plots to estimate the amount and distribution of aboveground biomass in the boreal forest of North America

“…ICESat-2 will use the Advanced Topographic Laser Altimeter System (ATLAS) micropulse, multibeam, photon-counting lidar that has a lower energy, but a higher repetition rate, than the analog waveform system used on ICESat (Herzfeld et al 2014). A secondary mission objective for ICESat-2 is to provide measurements of vegetation height at a maximum between-adjacent-orbit spacing of <2 km.…”

Land-ice elevation changes from photon-counting swath altimetry: first applications over the Antarctic ice sheet

“…These reductions enable the transmission of multiple discrete beamlets, with echoes received on individual counting cells, to cover both broad swaths of terrain and improved detection statistics. The scanning PCL system (Degnan and others, 2007;Herzfeld and others, 2014) from which our PCL was derived was originally developed as an outerplanets exploration test bed, then adapted for deployment on unmanned airborne vehicles. The ability to deploy a lightweight instrument with multiple lidar beamlets was a fundamental driver of the decision to use a photon-counting system, ATLAS, on ICESat-2 (Wu and others, 2010).…”

Analysis of MABEL Bathymetry in Keweenaw Bay and Implications for ICESat-2 ATLAS

“…Only with advances in photon-detector ranging resolution and dead time have photon-counting systems become viable mapping tools [40]. A number of recent publications target terrestrial and cryospheric applications, such as canopy extraction [41][42][43] and sea-ice and glacier profiling [44][45][46][47], and noise-filtering techniques [48][49][50], but research pertaining to using photon-counting lidar for bathymetric mapping remains limited.…”