Coherent Change Detection Under a Forest Canopy

Coherent change detection (CCD) is an established technique for remotely monitoring landscapes with minimal vegetation or buildings. By evaluating the local complex correlation between a pair of synthetic aperture radar (SAR) images acquired on repeat passes of an airborne or spaceborne imaging radar system, a map of the scene coherence is obtained. Subtle disturbances of the ground are detected as areas of low coherence in the surface clutter. This thesis investigates extending CCD to monitor the ground in a forest. It is formulated as a multichannel dual-layer coherence estimation problem, where the coherence of scattering from the ground is estimated after suppressing interference from the canopy by vertically beamforming multiple image channels acquired at slightly different grazing angles on each pass. This 3D SAR beamforming must preserve the phase of the ground response. The choice of operating wavelength is considered in terms of the trade-off between foliage penetration and change sensitivity. A framework for comparing the performance of different radar designs and beamforming algorithms, as well as assessing the sensitivity to error, is built around the random-volume-over-ground (RVOG) model of forest scattering. If the ground and volume scattering contributions in the received echo are of similar strength, it is shown that an L-band array of just three channels can provide enough volume attenuation to permit reasonable estimation of the ground coherence. The proposed method is demonstrated using an RVOG clutter simulation and a modified version of the physics-based SAR image simulator PolSARproSim. Receiver operating characteristics show that whilst ordinary single-channel CCD is unusable when a canopy is present, 3D SAR CCD permits reasonable detection performance. A novel polarimetric filtering algorithm is also proposed to remove contributions from the ground-trunk double-bounce scattering mechanism, which may mask changes on the ground near trees. To enable this kind of polarimetric processing, fully polarimetric data must be acquired and calibrated. Motivated by an interim version of the Ingara airborne imaging radar, which used a pair of helical antennas to acquire circularly polarised data, techniques for the estimation of polarimetric distortion in the circular basis are investigated. It is shown that the standard approach to estimating cross-talk in the linear basis, whereby expressions for the distortion of reflection-symmetric clutter are linearised and solved, cannot be adapted to the circular basis, because the first-order effects of individual cross-talk parameters cannot be distinguished. An alternative approach is proposed that uses ordinary and gridded trihedral corner reflectors, and optionally dihedrals, to iteratively estimate the channel imbalance and cross-talk parameters. Monte Carlo simulations show that the method reliably converges to the true parameter values. Ingara data is calibrated using the method, with broadly consistent parameter estimates obtained across flights. Genuine scene changes may be masked by coherence loss that arises when the bands of spatial frequencies supported by the two passes do not match. Trimming the spatial-frequency bands to their common area of support would remove these uncorrelated contributions, but the bands, and therefore the required trim, depend on the effective collection geometry at each pixel position. The precise dependence on local slope and collection geometry is derived in this thesis. Standard methods of SAR image formation use a flat focal plane and allow only a single global trim, which leads to spatially varying coherence loss when the terrain is undulating. An image-formation algorithm is detailed that exploits the flexibility offered by back-projection not only to focus the image onto a surface matched to the scene topography but also to allow spatially adaptive trimming. Improved coherence is demonstrated in simulation and using data from two airborne radar systems.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Electronic Engineering, 202

Inventário florestal : inferência por área ou por número de árvores?

Orientadora: Profa. Dra. Ana Paula Dalla CorteCoorientadores: Prof. Dr. Carlos Roberto Sanquetta, Prof. Dr. Alexandre BehlingTese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Agrárias, Programa de Pós-Graduação em Engenharia Florestal. Defesa : Curitiba, 19/08/2021Inclui referênciasÁrea de concentração: Manejo FlorestalResumo: O volume total de uma população florestal é estimado por meio de técnicas de amostragem utilizadas nos inventários florestais, em que o volume estimado na área da unidade amostral é extrapolado para a área do talhão. Neste trabalho, o objetivo foi avaliar e comparar dois métodos para a estimativa do volume total em florestas plantadas: 1) método tradicional de inventários florestais (inferência por área); e 2) método de árvore individual, no qual a estimativa é realizada pelo produto do volume médio individual (vmi) pelo número de árvores detectadas remotamente nos talhões (inferência por indivíduo). A pesquisa foi conduzida em três talhões florestais: Pinus taeda (16 anos), Pinus taeda (7 anos) e Eucalyptus urograndis (5 anos). Em cada talhão, foi realizado o censo para as variáveis: diâmetro a 1,30 m e altura total. Os volumes das árvores foram estimados pelo modelo de Schumacher-Hall, ao passo que a soma dos seus volumes individuais foi considerada como o volume total paramétrico. Em seguida, foi executada a etapa da estimativa do volume total da população. No método 1 (por área), foram analisados dois procedimentos de amostragem (aleatória simples e sistemática). No método 2 (por número de árvores), o vmi utilizado foi obtido de duas maneiras: (a) média do volume individual de cem árvores selecionadas aleatoriamente, reamostradas pelo método Bootstrap e, (b) pela amostragem sistemática. O número de árvores (N) foi obtido por um algoritmo de contagem automática aplicado em imagens obtidas por -uma aeronave remotamente pilotada (ARP). Adicionalmente, no método 2, foram simuladas diferentes taxas de detecção de indivíduos (90% a 110%), enquanto para o método 1, foram simuladas diferenças (±10%) na área do talhão. Os resultados dos dois métodos de estimativa de volume total da população foram comparados ao volume total paramétrico pela diferença absoluta, diferença relativa e pela abrangência dos intervalos de confiança obtidos por cada método. O método 1, tradicional de inventário florestal (inferência por área), apresentou as menores diferenças em relação ao volume do censo. O processo de amostragem sistemático produziu os melhores resultados para os talhões 1 e 3, enquanto o processo aleatório foi o melhor para o talhão 1. O método 2 (abordagem por número de árvores) apresentou o volume total paramétrico dentro do intervalo de confiança (95% de probabilidade) ao se utilizar o vmi da amostragem aleatória de cem árvores e o número de árvores detectadas automaticamente, com diferença relativa de no máximo 4,7%. A variação em área e em número de árvores permitiu verificar que o acerto em 100% da área ou em 100% da do número de árvores não garante o menor erro de estimativa para o total, pois ela também depende da acurácia da estimativa do volume médio individual. O método 2 (abordagem por número de árvores) pode ser utilizado como uma alternativa ao inventário florestal tradicional.Abstract: The total volume of a forest population is estimated through sampling techniques used in forest inventories, in which the estimated volume in the sample unit area is extrapolated to the stand area. The aim of this work was to evaluate and compare two methods for estimating the total volume in planted forests: 1) traditional method of forest inventories (inference by area); and 2) individual tree method, in which the estimate is performed by the product of the mean individual volume by the number of trees remotely detected in the stands (inference by number of trees). The study was conducted in three forest stands: Pinus taeda (16 years of age), Pinus taeda (7 years of age) and Eucalyptus urograndis (5 years of age). A census was carried out in each stand for the variables: diameter at 1.30 m (d) and total height. Tree volumes were estimated by the Schumacher-Hall's model and the sum of their individual volumes was considered as the total parametric volume. Then, the step for estimating the total population volume was performed. Thus, two sampling procedures (simple random and systematic) were analyzed in method 1 (by area). Next, the mean individual volume used in method 2 (number of trees) was obtained in two ways: (a) mean individual volume of one hundred randomly selected trees, resampled by the Bootstrap method; and (b) by systematic sampling. The number of trees (N) was obtained by an automatic counting algorithm applied to images obtained by RPA. Additionally, different detection rates of individuals (90% to 110%) were simulated in method 2, while differences (±10%) in the stand area were simulated for method 1. The results of the two methods for estimating total population volume were compared to the total parametric volume by the absolute difference, relative difference and by the amplitude of the 95% confidence intervals obtained by each method. Method 1, traditional forest inventory (inference by area), showed the smallest differences in relation to the volume of the census. The systematic sampling process produced the best results for plots 1 and 3, and the random process for plot 1. Method 2 (number of trees) presented the total parametric volume included in the confidence interval when using the mean individual volume of random sampling of one hundred trees and the number of trees automatically detected, with a relative difference of at most 4.7%. The variation in area and number of trees enabled us to verify that the correctness in 100% of the area or in 100% of the number of trees does not guarantee the smallest estimate error for the total, as it depends on the accuracy of the estimate of the average volume individual. Method 2 (number of trees) can be used as an alternative to the traditional forest inventory

Demonstration of Single-Pass Millimeterwave SAR Tomography for Forest Volumes

In this letter, for the first time, the potential of millimeterwave synthetic aperture radar (SAR) is investigated with respect to a tomographic analysis of forest volumes. Exploiting both parametric and nonparametric SAR tomography (TomoSAR) methods designed for both discrete and continuous reflectivity profiles, it is shown that even Ka-band signals with a wavelength of only 8.55 mm can penetrate the tree canopy to a certain extent and allow a separation of ground and tree crowns. First experimental results exploiting airborne multiantenna data are evaluated with respect to LiDAR ground truth and indicate a promising perspective

Electromagnetic characterization of barefaced terrain for oil sand exploration

The scant difference in the electromagnetic (EM) reflectivity of barefaced terrain often imposes challenges in differentiating between such terrain types and deployment of synthetic aperture radar to oil sand exploration. Microwave remote sensing has a proven ability to provide valuable information about targets. However to derive geoscientific information, a profound understanding of the EM interaction with terrain is vital. The challenge is to identify scattering characteristics relevant to oil sand fields. While various terrain identification methods and signature databases have been developed in the optical domain, only few examples of barefaced terrain discrimination in the microwave domain have been reported. In this thesis a three step multi-sensor approach has been used to identify EM signature of barefaced terrain encompassing homogeneous and heterogeneous materials, in the optical and microwave range. The combined method also led to the development of a large database of hyperspectral reflectivity, dielectric and backscattering data relevant to geointelligence analysis. The geochemical signature identification and prediction (GSIP) process required spectral data acquisition, chemometric model implementation and postprocessing to determine the spectral fingerprints and components of two strains of Nigerian oil sands. The results were compared with available hydrocarbon databases and four new features of Nigerian oil sands were observed. The dielectric discrimination statistical model (DDSM) involved three studies of the dielectric properties of oil sands and other barefaced terrain with different weight percentage of moisture and statistical processing of data to identify the 1 – 2 GHz and 5 – 7 GHz as most suitable frequency bands for microwave imaging. The GSIP and DDSM provided new empirical data on the geochemical and electrical behaviour of oil sand particularly the contrasting effects of bitumen, sand and moisture. Finally computer EM (CEM) models of barefaced terrain and sensors were used to identify the backscattering behaviour of the terrain for analysis in 2D/3D format. The results provided good agreement with classical surface roughness models particularly the Surface Perturbation and Kirchoffs Scattering model. They also enabled the investigation of the effect of wide variations in the sensor and terrain parameters on backscattering in order to evolve a radar signature necessary for identification of oil sand terrain for petroleum exploration. A laboratory scatterometer system (LSS) was developed and deployed in three imaging scenarios to verify aspects of the derived microwave EM signature of the terrain. The LSS measurements and the results from the CEMs were complimentary

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion