Harvard Forest Research

Retrieval of Forest Structure using an Undercanopy, Upward-Scanning Lidar

Principal Investigator: Alan Strahler
Boston University: Jan 01 2007 - Jan 01 2010:

Abstract:
We would like to acquire additional data at Harvard Forest using the Australian Echidna® lidar, an under-canopy scanning lidar instrument that retrieves various measurements of forest structure and provides a 3-D reconstruction of the forest using multiple overlapping forest scans.

The instrument, developed by CSIRO Australia, is a prototype called the Echidna Validation Instrument or EVI. It uses a horizontally-mounted 1064 nm laser that sends pulses to a rotating 45-degree-angled mirror, thus scanning in a vertical circle. The instrument, which is tripod-mounted and a little larger than a rural mailbox, then rotates on its vertical axis, allowing the vertical circle to scan the full hemisphere and beyond within a few minutes. A photodetector measures the lidar return, digitizing the full waveform received from each outgoing pulse. The waveform data allow the retrieval of many canopy structural properties, including stand basal area, tree diameter distribution, foliage profile, and leaf area index.

Our research is supported by NASA under grant NNG06GI92G to Boston University with a subcontract to Hunter College of the City University of New York. The main thrust of the grant is to improve the remote retrieval of vegetation structural parameters by coupling undercanopy measurements from the EVI with downlooking aircraft lidar from NASA’s Laser Vegetation Imaging Sensor (LVIS) and downlooking spacecraft lidar from NASA’s Geoscience Laser Altimeter System (GLAS). The coupling will use a unified model of lidar scattering, termed GORT-Lidar, to merge observations from all three levels into a tool for retrieval of canopy structural parameters over broad regions.

To accomplish this goal, we acquired EVI lidar data at HF in the summer of 2008 at two sites in the Prospect Hill Tract: the old hemlock plantation, and in a young deciduous stand in Walter Lyford’s Woods. We successfully retrieved such parameters as means stem diameter; stem count density; stand height; biomass; and leaf area index from the lidar scans. The results are reported in a manuscript submitted for publication in January, 2009. Our results were also reported in a poster at the recent Harvard Forest Research Symposium, at which we showed a three-dimensional representation of a portion of the old hemlock plantation.

We would like to return to the forest in 2010, acquiring more lidar scans over a three-day period in late July or early August. During this time, we will acquire scans of two or three sites in the Prospect Hill Tract. Our objective will be to reconstruct two or three forest stands of about 1 ha in size from overlapping lidar scans using a simple tomographic approach. We will also make nondestructive measurements of a sample of trees, including tree species, DBH, distance from the point to the tree, tree height, canopy position, live/dead status, and crown shape. LAI measurements, using a LICOR LAI-200, will also be acquired within the stand, as well as hemispherical photos used to retrieve LAI. We will also make spectral reflectance measurements of leaves, bark, litter, and other objects using VNIR spectrometers.

The EVI is rated as a class 3R laser according to Australian/New Zealand Standard (AS/NZS) 2211.1:2004. This standard has been reproduced from International Standard IEC 60825-1:200. A category 3R laser is eye safe unless viewed from a short distance (<30 m) using an optical magnifying instrument (i.e., binoculars). The standard operating procedures require posting of warning signs at a 30 m distance from the instrument on obvious paths of entry. We will obtain necessary documentation and/or registration of the instrument for legal opoeration according to health and safety codes of Massachusetts.

We will contact HF as soon as our plans are finalized to coordinate activities.

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