The Pyla 2001 Experiment: Evaluation of Polarimetric Radar Capabilities over a Forested Area (original) (raw)

The effect of soil and crop residue characteristics on polarimetric radar response

Remote Sensing of Environment, 2002

Although the interaction between linear polarized microwaves and agricultural targets has been studied extensively, far less is understood about the added information provided from polarimetric Synthetic Aperture Radars (SARs). Using 1994 Spaceborne Imaging Radar-C (SIR-C) data, this study examines the sensitivity of linear polarizations and polarimetric parameters to conditions present on agricultural fields during the period of preplanting and post harvest. The polarimetric parameters investigated include circular polarized backscatter, pedestal height, and co-polarized phase differences (PPD). The co-polarization signature plots are also discussed. Results indicate that the dominant scattering mechanism from these fields varies depending on the type and amount of residue cover, and whether the crop had been harvested. Radar parameters most sensitive to volume and multiple scattering perform best at characterizing these surface conditions. These parameters are the pedestal height, as well as the linear crosspolarization (HV) and the circular co-polarization (RR). The co polarization signature plots and the standard deviation associated with the PPD are also useful in categorizing these cover types. However, the field average PPD provides little information on residue and soil characteristics.

The application of C-band polarimetric SAR for agriculture: a review

Canadian Journal of Remote Sensing, 2004

Agricultural targets are very dynamic throughout the growing season, and thus remote sensing is an attractive approach to mapping and monitoring applications. Research performed with synthetic aperture radar (SAR) satellite systems such as European Remote Sensing Satellites ERS-1 and ERS-2, Japanese Earth Resources Satellite 1 (JERS-1), and RADARSAT-1 has demonstrated the potential of using this approach for a wide variety of applications. These satellites all have single-channel radars, however, and the research often concluded that additional channels and multitemporal observations were required. Spaceborne imaging radar C/X-band synthetic aperture radar (SIR-C/X-SAR) demonstrated this approach but was limited to two flight periods for data collection and a relatively small number of sites. RADARSAT-2 will have multipolarization and polarimetric modes and higher resolution than RADARSAT-1. ENVISAT advanced synthetic aperture radar (ASAR) also has a multipolarization capability. These sensors will allow further development of applications in agriculture, particularly crop-type mapping and condition assessment, soil tillage and crop residue mapping, and soil moisture estimation. Research has demonstrated that the additional polarizations will increase the information content in a SAR dataset similar to using multispectral approaches in the optical region. The value of the phase information and the polarimetric parameters that can be derived from these data is less certain. However, this information does help in understanding the scattering mechanisms and target interactions that are occurring, leading to a better approach to data processing and information extraction. Integrating C-band SAR with data acquired at other radar frequencies, or with data acquired by optical sensors, can provide additional crop and soils information. This paper reviews the use of C-band polarimetric and multipolarization data for agricultural applications with an emphasis on the potential of the upcoming RADARSAT-2 system.

A dual-low-frequency radar for sub-canopy and deep soil-moisture measurements

Dna Repair, 2003

Measurements of deep and sub-canopy soil moisture are critical in understanding the global water and carbon energy cycle, but are not presently available on a synoptic basis. In this paper, we discuss a proposed spaceborne dual-frequency (UHF and VHF) radar that can provide globally these key measurements. This system is polarimetric and the low transmit frequencies chosen for their penetration abilities necessitate a large antenna that has an aperture of approximately 30m by 1 lm at VHF, and 30m by 3m at UHF. We describe the mission concept, overall system design and performance characteristics, and discuss ongoing tasks to prototype key system components, and verify the retrieval algorithm. We are also developing a tower-based prototype radar system. This system will, through field observations, demonstrate the scientific effectiveness of the measurement concept and provide critical data for algorithm development. We provide details of the ground experimentation including issues u...

Inference of forest biomass using P-band circular-polarized radar signals

Proceedings of IGARSS '94 - 1994 IEEE International Geoscience and Remote Sensing Symposium, 1994

In three sites of boreal and temperate forests, P band HH, HV, and VV polarization data combined estimate total aboveground dry woody biomass within 12 to 27% of the values derived from allometric equations, depending on forest complexity. Biomass estimates derived from HV-polarization data only are 2 to 14% less accurate. When the radar operates at circular polarization, the errors exceed 100% over flooded forests, wet or damaged trees and sparse open tall forests because doublebounce reflections of the radar signals yield radar signatures similar to that of tall and massive forests. Circular polarizations, which minimize the effect of Faraday rotation in spaceborne applications, are therefore of limited use for measuring forest biomass. In the tropical rain forest of Manu, in Peru, where forest biomass ranges from 4 kg m-' in young forest succession up to 50 kg m-' in old, undisturbed floodplain stands, the P band horizontal and vertical polarization data combined separate biomass classes in good agreement with forest inventory estimates. The worldwide need for large scale, updated, biomass estimates, achieved with a uniformly applied method, justifies a more in-depth exploration of multi-polarization long wavelength imaging radar applications for tropical forests inventories. Jakob J. van Zyl (S'85-M'86) was born in Outjo. Namibia, in 1957. He received the Hons. B.Eng. degree cum laude in electronics engineering from the University of Stellenbosch, Stellenbosch. South

Multi-frequency and multi-polarized SAR response to thin vegetation and scattered trees

This communication highlights the results of a study carried out to understand the Synthetic Aperture Radar (SAR) response to thin vegetation volume at L, C and X bands as well as cross-polarizations at L and C bands, and the X band at VV polarization. The sensitivity of SAR backscatter to the vegetation volume varies with the frequency, polarization and incidence angle at which the canopy is illuminated. Multifrequency, multi-polarized SAR response of thin linear vegetation along the roadside, small thorny hedges along the boundary of the farmers’ fields and scattered cluster of trees was studied for this purpose. It was observed that cross-polarized signals were able to pick up signals better from a very thin vegetation volume among the polarization responses and the L band was the most sensitive among the frequencies.

Applications of low-frequency SAR. Executive Summary

2004

This report details the work performed within the ALFS (Applications of Low-Frequency SAR) project. The project investigated the needs for forest biomass and soil moisture mapping, and the potential of a spaceborne P-band (435MHz) synthetic aperture radar (SAR) to meet those needs. Through a detailed study of published results, investigation of archived data from test-sites, backscatter modelling, and simulation of SAR system performance (including the important effects of ionospheric propagation), the ability of a P-band SAR satellite to meet user requirements has been evaluated. Forest applications have been investigated using AIRSAR data from the boreal forest and tropical forests in the Amazon basin and Indonesia. For boreal forests, the main application envisaged is the mapping of broad biomass classes. The results show that even a spaceborne SAR should be able to provide reliable maps of biomass classes. In some cases the biomass may be retrieved more accurately, but in general variations of tree number density preclude this, unless additional information is available to complement the P-band backscatter measurements. For tropical forests, the P-band backscatter can be used directly to differentiate between areas of high and low biomass. Moreover, the P-band data shows variations in high biomass forest that are related to the structure and flooding condition, some of which are not visible in Lband SAR images. A P-band SAR satellite is therefore expected to be the only method for mapping these variations, which can be related to forest structural types and give an indication of biomass. For soil moisture mapping, the test-sites studied show some correlation between the co-polarized backscatter ratio (HH/VV) and the soil moisture content. However, the low backscatter levels is easily disturbed by interference from strong scatterers, and while airborne SAR data is difficult to interpret, spaceborne SAR will be even harder. The possibility to map temporal changes of moisture is one possible application of P-band data, that has not studied in this project. The studies of the technical challenges involved in P-band SAR indicate that they can be overcome sufficiently well to provide data useful for forestry applications. The studies indicate that full polarimetric measurements should be provided to meet the needs for the applications.

Exploration of Factors Limiting Biomass Estimation by Polarimetric Radar in Tropical Forests

IEEE Transactions on Geoscience and Remote Sensing, 2004

Direct inversion of radar return signals for forest biomass estimation is limited by signal saturation at medium biomass levels (roughly 150 ton/ha for P-band). Disturbing factors such as forest structural differences-and, notably, at low biomass levels, terrain roughness, and soil moisture variation-cause further complications. A new and indirect inversion approach is proposed that may circumvent such problems. Using multifrequency polarimetric radar the forest structure can be assessed accurately. Ecological relationships link these structures with biomass levels, even for high biomass levels. The LIFEFORM model is introduced as a new approach to transform field observations of the complex tropical forest into input files for the theoretical UTARTCAN polarimetric backscatter model. The validity of UTARTCAN for a wide range of forest structures is shown. Backscatter simulations for a wide range of forest structures, terrain roughness, and soil moisture clearly show the limitations of the direct approach and the validity of the proposed indirect approach up to very high levels of biomass.