Radar, Lidar and Vegetation Structure

Active Remote Sensing for Vegetation Studies

Greg Asner TED Talk

Using hyperspectral and active remote sensing together to address global change

Vegetation structural information, particularly in forests

Land cover mapping – used with spectral data or direct use of radar polarimetry

Agricultural mappingTropical vegetation studies under cloudy

skiesDeriving information on soil water content

Radar Applications for Vegetation Mapping and characterization

Radar can penetrate into plant canopies (pass through leaves, etc.) and reflect off of various parts of the plant

Longer wavelengths penetrate more deeply into the canopy than shorter wavelengths

By looking at the timing and intensity of radar backscatter from vegetation, can get information on the configuration of leaves, twigs, and trunks

Direct effects of vegetation on radar backscatter

The type of vegetationGrowth stageCondition and healthCrop yieldsAgricultural practicesSoil characteristics Disturbance type and intensityMany others…

Radar backscatter can indicate

Radar can be designed to transmit and receive EMR that is polarized

Characteristics of materials on the ground can change the polarization of radar signals (or not)

If you measure the amount of change in polarization, you can infer information about the materials on the surface

Radar Polarization

Different incident angles for radar change the amount of backscatter (reflectance)

By flying multiple passes of the same target but with different incidence angles, you can sometimes identify materials that otherwise would not be distinct.

Radar incident angle

Materials have a property called their dielectric constant that affects the amount of radar return

Water has a very high dielectric constantBy measuring the intensity of radar return

you can sometimes infer the water content of a material because of the effect of high dielectric constant on the radar signal

Soil Moisture

In general radar is useful for vegetation because…1. It can “see” through the canopy and give us

information on structure of plants2. It can be used to help identify plants that are

spectrally similar3. It can give us an idea of surface properties of

soils (e.g., water availability) which are related to vegetation

4. It can see through clouds in tropical areas Combining radar remote sensing with

optical remote sensing expands the possibilities for gathering information

Radar for vegetation -- summary

Can characterize structural feature of vegetation using LidarTree or shrub heightLeaf Area Index (LAI)Vegetation biomassCanopy structureFuel loadsCoarse woody debris

Lidar for Vegetation Studies

Multiple Lidar returns can give information about vegetation height and structure

Forest metrics

Biomass distribution in rain forest canopy. La Selva, Costa Rica

Map of canopy height and density in NE Utah – warm colors = trees, cool colors = brush

Lidar data are useful for creating high resolution surfacesSurface of top of plant canopyBare earth surfaceVegetation height by subtracting bare earth

from top of canopy surfaceDetailed topography maps are useful for

modeling vegetation distributionLidar is so high resolution that you can often

see individual trees and/or shrubs – can calculate things like vegetation density.

Lidar for vegetation – summary