Fjernmålingsbasert kartlegging og overvåking av tidevannssonen

Source at https://www.miljodirektoratet.no/publikasjoner/2021/mai-2021/satellite-based-national-intertidal-zone-mapping-of-continental-norway-with-sentinel-12/The report describes updated methods that were originally developed in Haarpaintner & Davids (2020) to map the intertidal zone, in terms of atmospheric exposure, type and areal extent, based on radar and optical high resolution (10m) satellite imagery from Sentinel-1A/B (C-band synthetic aperture radar, C-SAR) and Sentinel-2A/B (multi-spectral instruments) of the European Copernicus Program. It further presents the application of the method to create products covering the whole Norwegian coast, and describes some limitations and error sources. The project resulted in a first version of national products of the intertidal zone area, type and its atmospheric exposure

Time-frequency characterization of harmonizable random processes

In this thesis we study how to characterize nonstationary harmonizable random processes simultaneously in time and frequency. Unlike stationary random processes, harmonizable processes can have a frequency content that changes with time. Rather than working directly with the process itself, we analyze the second-order moment functions of the process and characterize the process from these moments. The second-order moments of a harmonizable process can be represented in the dual-time domain, the dual-frequency domain, the ambiguity domain and the time-frequency domain, where all domains are connected through Fourier transforms. The time-frequency domain often offers the most intuitive descriptions of the process, thus it will be the main focus of this thesis. We propose estimators of the time-frequency spectra, and we analyze the statistical properties of the estimators. The proposed estimators enjoy a great freedom in that they have many parameters that can be adjusted, and different choices of these parameters will be discussed. We demonstrate the estimator on both simulated complex-valued data and real-world real-valued data. The ambiguity domain is connected to the time-frequency domain through a 2-D Fourier transform. We can relate the support of the second-order moments in the ambiguity domain, which again is related to the concept of an underspread processes, to the smoothness of the time-frequency spectra. We propose an estimation procedure for the second-order moments in the ambiguity domain based on thresholding of empirical moments, as this will enable us to determine the support in this domain. The estimator is tested on simulated data, and we compare the estimated mean square error of our proposed estimator to a standard estimation approach. In order to provide objective and dimensionless representations of the time-frequency behavior of a harmonizable process, we define spectral coherence measures. The spectral coherences measure the correlation between the time behavior and frequency behavior of the process (time-frequency coherence) or the correlation across frequencies (dual-frequency coherence). We show how previously defined coherences may be obtained through a linear estimation scheme, and we propose alternative spectral coherence measures based on a widely linear estimation scheme. The time-frequency representations are applied to a specific stochastic problem, namely that of stochastic differential equations. By transforming the stochastic differential equation to the time-frequency domain and thus considering the second-order moments of the processes involved, we avoid the problems related to stochastic integration. We consider both random processes in time and random fields in spatial variables. We develop a general theory, and we consider both theoretical and simulated examples that corroborate the theory

The harmonizable representation of complex-valued nonstationary random processes

In this thesis we study the second-order statistical moment functions that characterizes complex-valued harmonizable processes. A real-valued harmonizable process has four Hermitian second-order functions. These functions are equivalent representations of the second-order statistical quantities of the process. For a complex-valued harmonizable process, however, we need the complementary functions in addition to the Hermitian functions to completely describe the second-order statistical behavior of the process. We define and discuss the Hermitian and the complementary functions of complex-valued harmonizable processes. Exact expressions for the Hermitian and complementary second-order moment functions for some important sub-classes of complex-valued harmonizable processes are derived and discussed. We introduce, test, and characterize numerical estimators of these functions. Numerically generated data, and a real-world earthquake data set, are employed to demonstrate that the estimators work in practice. Based on the concept of widely linear mean square estimation, we propose a novel generalized measure of coherence for harmonizable random processes. This measure generalizes a recently proposed measure of coherence based on linear mean square estimation. Finally, we argue that our alternative coherence measure may in fact be beneficial for most nonstationary processes, even for real-valued harmonizable processes

Multi-Temporal and Multi-Frequency SAR Analysis for Forest Land Cover Mapping of the Mai-Ndombe District (Democratic Republic of Congo)

The European Space Agency’s (ESA) “SAR for REDD” project aims to support complementing optical remote sensing capacities in Africa with synthetic aperture radar (SAR) for Reducing Emissions from Deforestation and Forest Degradation (REDD). The aim of this study is to assess and compare Sentinel-1 C-band, ALOS-2 PALSAR-2 L-band and combined C/L-band SAR-based land cover mapping over a large tropical area in the Democratic Republic of Congo (DRC). The overall approach is to benefit from multi-temporal observations acquired from 2015 to 2017 to extract statistical parameters and seasonality of backscatters to improve forest land cover (FLC) classification. We investigate whether and to what extent the denser time series of C- band SAR can compensate for the L-band’s deeper vegetation penetration depth and known better FLC mapping performance. The supervised classification differentiates into forest, inundated forest, woody savannah, dry and wet grassland, and river swamps. Several feature combinations of statistical parameters from both, single and multi-frequency observations in a multivariate maximum-likelihood classification are compared. The FLC maps are reclassified into forest, savannah, and grassland (FSG) and validated with a systematic sampling grid of manual interpretations of very-high-resolution optical satellite data. Using the temporal variability of the dual-polarized backscatters, in the form of either wet/dry seasonal averages or using the statistical variance, in addition to the average backscatter, increased the classification accuracies by 4–5 percent points and 1–2 percent points for C- and L-band, respectively. For the FSG validation overall accuracies of 84.4%, 89.1%, and 90.0% were achieved for single frequency C- and L-band, and C/L-band combined, respectively. The resulting forest/non-forest (FNF) maps with accuracies of 90.3%, 92.2%, and 93.3%, respectively, are then compared to the Landsat-based Global Forest Change program’s and JAXA’s ALOS-1/2 based global FNF maps

Estimation of Ambiguity Functions With Limited Spread

This paper proposes a new estimation procedure for the ambiguity function of a non-stationary time series. The stochastic properties of the empirical ambiguity function calculated from a single sample in time are derived. Different thresholding procedures are introduced for the estimation of the ambiguity function. Such estimation methods are suitable if the ambiguity function is only non-negligible in a limited region of the ambiguity plane. The thresholds of the procedures are formally derived for each point in the plane, and methods for the estimation of nuisance parameters that the thresholds depend on are proposed. The estimation method is tested on several signals, and reductions in mean square error when estimating the ambiguity function by factors of over a hundred are obtained. An estimator of the spread of the ambiguity function is proposed

Satellite-Based National Intertidal-Zone Mapping of Continental Norway with Sentinel-1&2

The report describes updated methods that were originally developed in Haarpaintner & Davids (2020) to map the intertidal zone, in terms of atmospheric exposure, type and areal extent, based on radar and optical high resolution (10m) satellite imagery from Sentinel-1A/B (C-band synthetic aperture radar, C-SAR) and Sentinel-2A/B (multi-spectral instruments) of the European Copernicus Program. It further presents the application of the method to create products covering the whole Norwegian coast and describes some limitations and error sources. The project resulted in a first version of national products of the intertidal zone area, type and its atmospheric exposure.publishedVersio