| 1. |
- Fransson, JES, et al.
(författare)
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Estimation of forest parameters using CARABAS-II VHFSAR data
- 2000
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 38:2, s. 720-727
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Tidskriftsartikel (refereegranskat)abstract
- The use of airborne CARABAS-II VHF (20-90 MHz) SAR data for retrieval of forest parameters has been investigated, The investigation was performed at a test site located in the southwest: of Sweden consisting mainly of Norway spruce forests. Regression models predicting forest parameters from radar backscattering amplitude were developed and evaluated. The results showed a linear relationship between backscattering amplitude and forest stem volume, stem diameter, and tree height. The analysis also showed that the radar signal is strongly affected by ground slope conditions. The root mean square errors from the regression analysis, restricted to forest stands on near-horizontal ground, were found to be 66 m(3) ha(-1), 3.2 cm, and 2.3 m for stem volume, stem diameter, and tree height respectively. No saturation of the backscattered signal was observed up to the maximum stem volume of 625 m(3) ha(-1), corresponding to a biomass of 375 tons ha(-1). The results imply that VHF SAR data have significant potential for operational use in forestry.
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| 2. |
- Hellsten, H, et al.
(författare)
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Airborne array aperture UWBUHF radar - Motivation and system considerations
- 2000
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Ingår i: IEEE Aerospace and Electronic Systems Magazine. - 0885-8985 .- 1557-959X. ; 15:5, s. 35-45
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the necessity, feasibility, and technology of FOPEN GMTI. It argues that this functionality may be one mode in a multi-function UWB UHF system, which jointly possesses the capabilities for air target MTI and high resolution FOPEN SAR. The radar platform may be a UAV or an aircraft, whereas, we propose to use the push boom type of antenna mounting previously adopted with the advantage for the CARABAS II UWB VHF SAR. Presently, the push booms will hold a set of UWB UHF antenna elements. This paper relates GMTI to SAR, extended from imaging stationary ground to the 4-parameter set of targets in linear and uniform motion relative to ground. It is recognised that this extended imaging problem depends on one new parameter, i.e., the SAR focusing velocity. The required signal processing may be tackled in an efficient manner by a hierarchical scheme based on iteratively merging subapertures and increasing the resolution. Rejection of stationary clutter and detection occurs on all levels of increasing resolution. This paper also provides a brief presentation of the Swedish FOA efforts to produce an experimental demonstrator of this multi-function radar system.
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| 3. |
- Israelsson, H, et al.
(författare)
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A coherent scattering model to determine forest backscattering in the VHF-band
- 2000
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 38:1, s. 238-248
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Tidskriftsartikel (refereegranskat)abstract
- A coherent scattering model to determine the forest radar backscattering at VHF frequencies (20-90 MHz) has been de developed. The motivation for studying this frequency band is the recent development of the CARABAS Synthetic Aperture Radar (SAR). In order to model the scattering from branches and trunks, homogeneous dielectric cylinders placed above a semi-infinite dielectric ground have been analyzed. An analytical approach, where the theoretically exact currents induced in an infinite cylinder are truncated, has been compared to a numerical solution using the finite difference time domain (FDTD) method, If the first-order coherent ray tracing is included in the analytical approach, the results match well with the numerically exact FDTD solution. The results show that, in order to determine the VHF-backscattering from a forest stand, the coherent ground interaction is an important part and has to be considered. In this paper, modeling results are in good agreement with CARABAS measurements.
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| 4. |
- Luo, X, et al.
(författare)
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RFI suppression in ultra-wideband SAR systems using LMS filters in frequency domain
- 2001
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Ingår i: Electronics Letters. - 0013-5194 .- 1350-911X. ; 37:4, s. 241-243
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Tidskriftsartikel (refereegranskat)abstract
- A least-mean-square algorithm in the frequency domain, with amplitude normalisation. is proposed to remove narrowband radio frequency interference in low-frequency ultra-wideband synthetic aperture radar systems. The performance uf the algorithm was tested on experimental data acquired with the CARABAS system.
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| 5. |
- Smith, G, et al.
(författare)
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A model relating VHF-band backscatter to stem volume of coniferous boreal forest
- 2000
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 38:2, s. 728-740
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Tidskriftsartikel (refereegranskat)abstract
- A physical model is presented describing the backscatter from coniferous boreal forests in the lower VHF-band in terms of Stem volume. By using measurements of mean amplitude in high-resolution SAR images (rather than intensity), a linear dependence on stem volume can be obtained. The model fits well with the measurements made using the coherent all radio band sensing (CARABAS) SAR in the southern boreal forest, indicating the possibility of retrieving stem volume, and hence biomass, with an accuracy similar to that reached by standard ground-based measurements. No saturation of the scattering is seen up to biomasses of 550 m(3)/ha.
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