Eric S. Kasischke

Correlating radar backscatter with components of biomass in loblolly pine forests

A multifrequency, multipolarization airborne SAR data set was utilized to examine the relationship between radar backscatter and the aboveground biomass. This data set was also used to examine the potential of SAR to estimate aboveground biomass in these forests. The total aboveground biomass in the test stands used in this study ranged from >

The detection and mapping of Alaskan wildfires using a spaceborne imaging radar system

Abstract The study presented here focuses on using a spaceborne imaging radar, ERS-1, for mapping and estimating areal extent of fires which occurred in the interior region of Alaska. Fire scars are typically 3 to 6 dB brighter than adjacent unburned forests in the ERS-1 imagery. The enhanced backscatter from burned areas was found to be a result of high soil moisture and exposed rough ground surfaces. Fire scars from 1979 to 1992 are viewed in seasonal ERS-1 synthetic aperture radar (SAR) data obtained from 1991 to 1994. Three circumstances which influence the detectability of fire scars in the ERS-1 imagery are identified and examined; seasonality of fire scar appearances, fires occurring in mountainous regions, and fires occurring in wetland areas. Area estimates of the burned regions in the ERS-1 imagery are calculated through the use of a Geographic Information System (GIS) database. The results of this analysis are compared to fire records maintained by the Alaska Fire Service (AFS) and to estimates...

Mapping fire scars in global boreal forests using imaging radar data

This study is an extension of earlier research which demonstrated the utility of ERS SAR data for detection and monitoring of fire-disturbed boreal forests of Alaska. Fire scars were mappable in Alaska due to the ecological changes that occur post-burn including increased soil moisture. High soil moisture caused a characteristic enhanced backscatter signal to be received by the ERS sensor from burned forests. Since regional ecological differences in the global boreal biome may have an effect on post-fire ecosystem changes, it may also affect how fire scars appear in C-band SAR imagery. In the current study we evaluate the use of C-band SAR data to detect, map and monitor boreal fire scars globally. Study sites include four regions of Canada and an area in central Russia. Fire boundaries were mapped from SAR data without a priori knowledge of fire scar locations. SAR-derived maps were validated with fire service records and field checks. Based on results from test areas in Northwest Territories, Ontario, southeastern Quebec, and central Russia, C-band SAR data have high potential for use in detecting and mapping fire scars globally.

Observations of variations in ERS-1 SAR image intensity associated with forest fires in Alaska

Investigations have shown that fires in boreal forests result in characteristic responses which are recorded on ERS-1 SAR imagery. Using one of the many fire signatures observed on ERS-1 SAR imagery, the analysis of the data revealed there is >10 dB in variation in image intensity within the burned areas on the SAR images. Possible explanations for this variation include increases in soil moisture, increased surface roughness exposed to the incoming microwave radiation, and damage to the vegetation canopy by the fire. >

The effects of changes in forest biomass on radar backscatter from tree canopies

Abstract We validated a canopy backscatter model for loblolly pine forest stands at the Duke Forest, North Carolina, by comparing the observed and modelled SAR backscatter from the stands. Given the SAR backscatter data calibration uncertainty, the model made good predictions of C-HH, C-HV, L-HH, L-HV, L-VV, P-HH, and P-HV backscatter for most of 25 stands studied. The model overestimated C-VV backscatter for several stands, and largely overestimated P-VV backscatter for most of the stands. Using the collected SAR backscatter and ground data, and the backscatter model, we studied the influences of changes in biomass on SAR backscatter as a function of radar frequency and polarization, and evaluated the feasibility of deriving the biomass from the backscatter. This study showed that C-HH, C-HV, C-VV, L-VV, and P-VV SAR backscatter may be insensitive to the biomass change. L-HH, L-HV, P-HH, and P-HV SAR backscatter changed more than 5dB as the biomass varied. This study also showed that the L-HH and P-HH ba...

The effects of changes in loblolly pine biomass and soil moisture on ERS-1 SAR backscatter

Er young ( ~ the backscatter from the stands, and there was no significant correlation between the backscatter and biomass (r 2 = 0.19). Under dry soil conditions, the backscatter increased about 2-3 dB as the biomass increased from 0.05 kg/m 2 to about 0.51.5 kg/m ~, and the backscatter may be saturated near a 0.5-1.5 kg / m ~ biomass level. The correlation coe~cient between the backscatter and biomass was r 2 = 0.46. When the Santa Barbara microwave canopy backscatter model was applied to simulate the ERS-1 SAR backscatter from the stands over dry ground, modeled and observed backscatter had similar trends with increasing biomass. For these stands, sensitivity analyses using the model showed that as the surface-soil moisture increased, the major contributor to the total backscatter was changed from canopy volume scattering to surface backscatter between 0.4 kg / m 2 and about I kg/m 2. Signal saturating at low standing biomass and high sensitivity to soil moisture conditions limit the value of a short-wave (C-band) and steep local incidence angle (23 °) microwave sensor such as the ERS-1 SAR for forest monitoring.

The gridded trihedral: a new polarimetric SAR calibration reflector

The characteristics of the gridded trihedral used to calibrate polarimetric synthetic-aperture radar (SAR) systems are considered. The gridded trihedral is a normal trihedral with one of the conducting faces replaced with a grid of closely spaced (relative to a wavelength) parallel conductors over a layer of microwave absorber. This grid changes the incident waves polarization and results in a calibration target with a significant cross-polarized reflection. The advantages of the gridded trihedral are that it has a broad backscatter beamwidth (unlike the dihedral), and that it is passive and simple to construct (unlike the active radar calibrator, or ARC). The performance characteristics of the gridded trihedral reflector are reviewed, using basic theoretical models and calibrated P-3 SAR imagery. >

Assessing the influence of vegetation cover on soil-moisture signatures in fire-disturbed boreal forests in interior Alaska: Modelled results

A microwave backscattering model for shrub clumps was presented. The modelling approach was to treat the clumps as scatterers and attenuators. Three major model components were defined: surface backscattering, clump volume scattering, and multiple path interactions between clumps and ground. Total backscatter was computed by incoherent summation of the components. We then used the model to study the effects of variations in surface and willow properties (soil moisture content, and surface roughness rms height and correlation length, and willow ground coverage, clump height, and stem density) on backscatter from willows in Alaskan boreal forest region. We examined the sensitivity to variations of the six parameters combined and to variation of each parameter alone from willows of three clump sizes representing different stages of vegetation regrowth after fire. Modelled C-band backscatter was more sensitive to the variations of the surface and willow parameters than L-band backscatter at incidence angles between 20° and 60°. At incidence angles of 20-60°, C-HH and C-VV backscatter was sensitive to the variations of the three surface parameters. L-HV and L-VV backscatter were only sensitive to the moisture variation. Among the three willow parameters, change of willow ground coverage produced more sensitive cases than variations of clump height and stem density combined at C- and L-band.

Distribution of Forest Ecosystems and the Role of Fire in the North American Boreal Region

The boreal biome is characterized by several limiting factors that not only restrict species diversity and levels of primary productivity but also control specific processes in boreal ecosystems. These limiting factors include short growing seasons, low soil temperatures, extreme seasonal fluctuations in day length and temperature, continuous and discontinuous permafrost conditions, and the predominance of fire. This chapter synthesizes research results, field experience, and literature reviews to assess the influence of these abiotic factors on the boreal forests of North America. It provides information on the geology, ecology, soils, vegetation, and fire regimes of these forests.

A digital calibration method for synthetic aperture radar systems

A basic method to calibrate imagery from synthetic aperture radar (SAR) systems is presented. SAR images are calibrated by monitoring all the terms of the radar equation. This procedure includes the use of both external (calibrated reference reflectors) and internal (system-generated calibration signals) sources to monitor the total SAR system transfer function. To illustrate the implementation of the procedure, two calibrated SAR images (X-band, 3.2-cm wavelength) are presented, along with the radar cross-section measurements of specific scenes within each image. The sources of error within the SAR image calibration procedure are identified. >