Kjell Arild Høgda

NORCE Norwegian Research Centre · Technology

Interferometric Synthetic Aperture Radar (InSAR) remote sensing generally lacks deformation sensitivity in the along-track direction. In this proposed approach, across-track observations from conventional InSAR, using both ascending and descending passes, were superimposed with the along-track movement derived from multi-aperture InSAR (MAI) to det...

Remarkable developments in the fields of earth observation (EO) satellites and remote sensing (RS) technology over the past four decades have substantially contributed to spatial, spectral, and temporal sampling [...]

Svalbard Integrated Arctic Earth Observing System (SIOS) is an international partnership of research institutions studying the environment and climate in and around Svalbard. SIOS is developing an efficient observing system, where researchers share technology, experience, and data, work together to close knowledge gaps, and decrease the environment...

Monitoring water storage in lakes and reservoirs is critical to water resource management, especially in a changing climate. Satellite microwave remote sensing offers a weather and light-independent solution for mapping water cover over large scales. We have used 13 years of synthetic aperture radar (SAR) data from three different sensors (Sentinel...

In this article, we have presented surface velocity estimation of Chhota Shigri (CS) and Bara Shigri (BS) glaciers in the Himalaya using C-band synthetic aperture radar (SAR) data from Sentinel-1 (S-1). Repeat-pass SAR image subpixel offset tracking has been used to generate velocity vectors from yearly and seasonal S-1 data sets. SAR offset tracki...

Slab avalanches release due to failure in a weak snow layer. Determining the spatial distribution and depth of weak layers in avalanche starting zones are high-risk tasks. Moreover, by manually digging snow pits, the occurrence of a weak layer can only be identified on a pit scale (meters). We therefore propose a technical solution to this problem...

Satellite-aided studies of vegetation cover, biomass and productivity are becoming increasingly important for monitoring the effects of a changing climate on the biosphere. With their large spatial coverage and good temporal resolution, space-borne instruments are ideal to observe remote areas over extended time periods. However, long time series d...

Monitoring and understanding climate-induced changes in the boreal and arctic vegetation is critical to aid in prognosticating their future. We used a 33 year (1982–2014) long record of satellite observations to robustly assess changes in metrics of growing season (onset: SOS, end: EOS and length: LOS) and seasonal total gross primary productivity....

Use of Unmanned Aircraft Systems (UAS) gives the opportunity to carry out research with a re-duced environmental footprint. Unmanned aircraft, including both fixed wing and multi rotor types (helicopters) allow us to collect very high resolution image data for vegetation mapping without the need for any personnel walking into the site and thereby p...

The Arctic is among the regions with the most rapid changes in climate and has the expected highest increase in temperature. Changes in the timing of phenological phases, such as onset of the growing season observed from remote sensing, are among the most sensitive bio-indicators of climate change. The study area here is the High Arctic archipelago...

The release of cold temperature constraints on photosynthesis has led to increased productivity (greening) in significant parts (32–39%) of the Arctic, but much of the Arctic shows stable (57–64%) or reduced productivity (browning, <4%). Summer drought and wildfires are the best-documented drivers causing browning of continental areas, but factors...

Large-scale geographical variation in phenotypic traits within species is often correlated to local environmental conditions and population density. Such phenotypic variation has recently been shown to also be influenced by genetic structuring of populations. In ungulates, large-scale geographical variation in phenotypic traits, such as body mass,...

Global temperature is increasing, and this is affecting the vegetation phenology in many parts of the world. In Fennoscandia, as well as Northern Europe, the advances of phenological events in spring have been recorded in recent decades. In this study, we analyzed the start of the growing season within five different vegetation regions in Fennoscan...

We estimate two-dimensional (2D) glacier surface motion using synthetic aperture radar (SAR) X-band intensity tracking. It has been observed that the viability of SAR interferometry (InSAR) is often limited by coherence loss over glaciers in landlocked regions using SAR data pairs of more than 1 day temporal baseline. An alternative to InSAR is the...

The section about monitoring covers the development of phenological networks, remote sensing of the season cycle of the vegetation, the emergence of the science of aerobiology and, more specifically, aeropalynology, pollen sampling instruments, pollen counting techniques, applications of aeropalynology in agriculture and the European Pollen Informa...

Populations can vary considerably in their response to environmental fluctuations, and understanding the mechanisms behind this variation is vital for predicting effects of environmental variation and change on population dynamics. Such variation can be caused by spatial differences in how environmental conditions influence key parameters for the s...

In this paper, we propose a method to monitor the extent of different facies on glaciers on Svalbard. The extent of the firn facies can be used as an indicator for trends in mass balance. We produce an averaged image from Envisat ASAR wide swath mode scenes for an entire winter season. The averaged image is segmented into three classes using a Gaus...

Use of all-terrain vehicles (ATVs) in vulnerable environments may cause vegetation and soil erosion that will last for a long time. In northern parts of Norway, the growing use of ATVs off-road has made considerable damage to the environment. In Troms County, the Norwegian Army has exercise and shooting ranges (battlefields) where there has been ex...

Spaceborne repeat pass Synthetic Aperture Radar (SAR) interferometry (InSAR)is a precision deformation measurement tool. InSAR provides high resolution terrain displacement map associated with many geophysical processes. Advanced DInSAR approaches are able to quantify mm to cm level deformation signals by involving a time series SAR images and thei...

In this study ascending and descending passes interferometric synthetic aperture radar (InSAR) techniques are used for glacier surface velocity estimation in the Himalaya. Single-track interferometric measurements are sensitive to only a single component of the three dimensional (3-D) velocity vectors. European Remote Sensing satellites (ERS-1/2) t...

We have used the repeat pass Synthetic Aperture Radar (SAR) intensity tracking for two dimensional (2-D) glacier surface motion estimation using X-band data. It has been observed that the viability of SAR interferometry (InSAR) often is limited by coherence loss over glaciers in land locked regions using SAR data pairs of more than one-day temporal...

Question: Is there a need for disturbance mapping integrated in the CircumBoreal Vegetation Mapping Program? Location: Eurasian boreal forest. Disturbance and mapping: The boreal zone is characterized by a multitude of natural and anthropogenic disturbance agents with importance over a wide range of spatial and temporal scales. Disturbance is a pri...

Annual variation in the environment is expected to influence individual performance, e.g. measured as body condition, Such as body mass or fat deposition, through its direct or indirect effects on food abundance and availability. Such environmental variation is traditionally Measured by climatic observation, but recently, measures of environmental...

The study area of Fermoscandia is a heterogeneous climatic region. To map the linear trends in onset, end, and length of the growing season in Fermoscandia, the bimonthly Global Inventory Modeling and Mapping Studies (GIMMS) normalized difference vegetation index (NDVI) satellite data set was used. The data set has an 8 x 8 km(2) spatial resolution...

Defoliation caused by repeated outbreaks of cyclic geometrid moths is the most prominent natural disturbance factor in the northern-boreal birch forest. Evidence suggests that recent changes in outbreak distribution and duration can be attributed to climate warming. There is hence an immediate need for methods that can be applied to characterize th...

In this study we present new satellite-based maps of the growing season of northern areas. The maps show trends and mean date in onset and length of the growing season at different scales north of 50° N. For all the circumpolar area we use the GIMMS-NDVI satellite dataset for the 1982 to 2006 period, and for the Nordic countries we used the MODISND...

In the multi-use landscape of southern Norway, the distribution of lynx is likely to be determined both by the abundance of their favoured prey – the roe deer – and the risk associated with the presence of humans because most lynx mortalities are caused by humans (recreational harvest, poaching, vehicle collisions). We described the distribution of...

Birch (Betulapubescens L.) is by far the most common deciduous tree in Norway and birch forests define the forest line both northwards and upwards. Because of its mountainous topography, long fjords, and long length from north to south, Norway is climatically and ecologically very diverse. Therefore, developing pollen forecasts in Norway is a chall...

In spring during 2004-07 we conducted ground-penetrating radar (GPR) measurements on the Austfonna ice cap, Svalbard, with the original aim of mapping the thickness and distribution of winter snow. Here, we further exploit the information content of the data and derive a multi-year sequence of glacier-facies distribution that provides valuable spat...

Birch forests cover large areas of the northern Fennoscandia and the mountain birch (Betula pubescens ssp. czerepanovii) often forming the altitudinal and Arctic forest and tree lines. Interpreting the factors leading to landscape changes in mountain birch forest involves disturbance from anthropogenic use and climate as important factors. Using ve...

An earlier onset of spring has been recorded for many parts of Eurasia in recent decades. This has consequences for migratory species, both in changing the conditions encountered by individuals on reaching migratory sites and in affecting cues regulating the timing of migration where decisions to migrate are influenced by local environmental variab...

We present a comparison between data acquired with frequency-modulated ground-penetrating radar (GPR) and satellite synthetic aperture radar (SAR). Both radars are polarimetric and operate at a center frequency of 5.3 GHz. The field site is the polythermal glacier Kongsvegen, Svalbard. Along glacier GPR profiles cover the ablation area and the accu...

Northern Fennoscandia is an ecologically heterogeneous region in the arctic/alpine-boreal transition area. Phenology data on birch from 13 stations and 16-day MODIS-NDVI composite satellite data with 250 m resolution for the period 2000 to 2006 were used to map the growing season. A new combined pixel-specific NDVI threshold and decision rule-based...

1. How climatic changes affect migratory birds remains difficult to predict because birds use multiple sites in a highly interdependent manner. A better understanding of how conditions along the flyway affect migration and ultimately fitness is of paramount interest. 2. Therefore, we developed a stochastic dynamic model to generate spatially and te...

An understanding of how species are affected by top-down and bottom-up processes in food webs, and how these forces interact with climatic conditions is crucial for how ecosystems should be managed. In Norway large carnivores are effectively removed from extensive areas to protect livestock, leaving human harvesting as the only significant top-down...

An NDVI dataset covering Fennoscandia and the Kola peninsula was created for vegetation and climate studies, using Moderate Resolution Imaging Spectroradiometer 16-day maximum value composite data from 2000 to 2005. To create the dataset, (1) the influence of the polar night and snow on the NDVI values was removed by replacing NDVI values in winter...

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extrac...

Fennoscandia is characterized by a large degree of climatic diversity. Vegetation phenology may respond differently to climate change according to the climatic gradients within the region. To map the annual and spatial variability of the start of the growing season (SOS) in Fennoscandia, the twice-monthly GIMMS-NDVI satellite dataset was used. The...

The question of penetration of synthetic aperture radar (SAR) signals at C-band frequency into polar glaciers is addressed by comparing ground penetrating radar (GPR) and SAR backscatter signatures. Profiles of the Kongsvegen glacier, Svalbard, were obtained with a C-band GPR. The received signal is converted to the equivalent radar cross section u...

The paper compares digital elevation models produced from spaceborne optical Ikonos images, airborne laser scanner data, airborne synthetic aperture radar images, and terrestrial digital camera images on Engabreen outlet glacier in Norway. The ground truth is given by a GPS profile all around on the glacier plateau and a network of ground control po...

This study has shown large regional differences in the changes of the length of the growing season, during the period 1982–1999 in Fennoscandia. It clearly indicates that the impact on length of growing season of global warming will be different depending on the regional climate. Whether the measured changes in spring and autumn events are caused b...

Intraspecific body mass in ungulates has often been shown to increase with latitude. The biological basis for such latitudinal gradients is, however, poorly known. Here we examined whether satellite-derived indices of environmental phenology, based on the normalised difference vegetation index (NDVI), as well as variables derived from meteorologica...

The phenophases first greening (bud burst) and yellowing of Nordic mountain birch (Betula pubescens ssp.tortuosa, also called B. p. ssp. czerepanovii) were observed at three sites on the Kola Peninsula in northernmost Europe during the period 1964-2003, and at two sites in the trans-boundary Pasvik-Enare region during 1994-2003. The field observati...

2-DE is a powerful technique to discriminate post-translationally modified protein isoforms. However, all steps of 2-DE preparation and gel-staining may introduce unwanted artefacts, including inconsistent variation of background intensity over the entire 2-DE gel image. Background intensity variations limit the accuracy of gel orientation, overlay...

A general problem in population ecology is to predict under which conditions stochastic variation in the environment has the stronger effect on ecological processes. By analysing temporal variation in a fitness‐related trait, body mass, in 21 Norwegian moose Alces alces (L.) populations, we examined whether the influence of temporal variation in di...

Aim To test whether satellite‐derived NDVI values obtained during the growing season as delimited by the onset of phenological phases can be used to map bioclimatically a large region such as Fennoscandia. Location Fennoscandia north of about 58° N and neighbouring parts of NW Russia. Methods Phenology data on birch from 15 research stations and th...

Spot shapes. Two images showing the difference in spot sizes between M0/M1/M2 and M4/M5 samples. The process of the changing spot distribution can be visualized by sorting all images according to their FAB classification and then showing them chronologically. This is visualized in a small movie. The two images and the movie are contained within a z...

Alignment accuracy. The correlation algorithm relies on the correct alignment of input images. This process is typically performed using calibration marks on gels. The additional data illustrates the importance of correct alignment.

Animated Correlation Method. A movie illustrating the correlation method made with blender [61]. The movie can be played with mplayer [62].

Correlation images illustrating impact of misclassification. The impact of wrong ALL versus AML diagnosis was examined by random swapping ALL and AML labels in the AML/ALL versus 2DE image correlations. This results in lower correlation values as expected.

Source material. The source material includes correlation analysis, image coloring, Gaussian bumps and the simulated images. The source is contained within a .html file. The algorithm is implemented in IDLv6.1 [60].

While factors affecting body growth have been extensively studied, very little is known about the factors likely to affect the sexual size dimorphism (SSD) in polygynous mammals. Based on the carcass mass of 24420 male and female moose recorded in 14 Norwegian populations, we examine three hypotheses to explain geographical variation in SSD. First,...

Current models of vegetation dynamics using the normalized vegetation index (NDVI) time series perform poorly for high-latitude environments. This is due partly to specific attributes of these environments, such as short growing season, long periods of darkness in winter, persistence of snow cover, and dominance of evergreen species, but also to th...

Two-dimensional gel electrophoresis (2DE) is a powerful technique to examine post-translational modifications of complexly modulated proteins. Currently, spot detection is a necessary step to assess relations between spots and biological variables. This often proves time consuming and difficult when working with non-perfect gels. We developed an an...

In this paper, we present the results achieved in the long-term subsidence project in Norway, ESA AO-1104, which have made use of ERS SAR data. By applying the differential SAR interferometry technique referred to as Small Baseline Subset (SBAS) approach to a test area covering the city of Oslo, Norway, we show significant subsidence in several are...

Implementation of a repeat-pass differential interferometric SAR (D-InSAR) processing facility is a challenging task, involving among other things a precise coregistration of two (or more) complex SAR images, removal of the contribution from topography using a Digital Elevation Model (DEM), and band-pass filtering of common bandwidth to reduce out-...

The paper present results from a series of European and national projects on remote sensing of snow parameters. Currently, satellite borne SAR data are only available at C-band frequencies. Other frequencies such as L-band or Ku-band may be favorable in several snow applications, but current C-band SAR may still be used and further developed to a m...

Current models of vegetation dynamics using the normalized vegetation index (NDVI) time series perform poorly for high-latitude environments. This is due partly to specific attributes of these environments, such as short growing season, long periods of darkness in winter, persistence of snow cover, and dominance of evergreen species, but also to th...

Climate change and particularly variations in air temperature have significant impacts on the growth rhythm of plants where these occur at the limits of their natural distribution range, especially at northern latitudes. Our study area, Fennoscandia and Kola Peninsula, is characterized by large regional climatic differences from south to north, fro...

Ground Penetrating Radar (GPR) operating at 5.3GHz (C-band), the same frequency as the Advanced Synthetic Aperture Radar (ASAR), is used to resolve the depth resolution not retrievable from the ASAR data. We present results from the first field season, April 2004. Two GPR instruments, one at 5.3GHz (C-Band) and the other at 800MHz, were used to tak...

The glacial firn line of the Svartisen Glacier has been detected using ERS II SAR and ENVISAT ASAR data from 1995 and up to today. The firn line is detected by first correcting the image backscatter intensity for topographic and geometric contributions using the Muhleman backscattering model. Then we discriminate between firn and ice facies based o...

In northern parts of Norway, the growing use of 4-wheel terrain motorcycles (light ATVs) outside roads is starting to damage the landscape. In Troms County, the Norwegian army has several exercise areas where there has been extensive use of light, medium and heavy armoured military vehicles and ATVs for decades. We have investigated the damage caus...

Estimation of total snow mass by means of SAR interfer-ometry is problematic, due to high sensitivity of the in-terferometric phase to the snow water equivalent, leading to the phase unwrapping problem. In this paper, we pursue a recently proposed technique, delta-k interferometric phase estimation, that avoids phase wrapping by lowering the sensit...

The study focuses on vegetation changes in the Nordic mountain birch forest in northern Norway, covering a period of more than 40 yr. The study area comprises the municipalities of Kautokeino and Karasjok on Finnmarkskvidda; it is predominantly covered by lichen and dwarf shrub vegetation. Sizes of various vegetation classes were estimated by the u...

The interferometric SAR (InSAR) technique may be a valuable tool for subsidence monitoring at different places of the Earth surface. Many results have been reported during the 1990 s where data from the ERS-1 and ERS-2 SAR sensors were used. This paper will present the ongoing long-term subsidence project in Norway, AO-1104, that are making use of...

The interferometric SAR (InSAR) technique may be a valuable tool for subsidence monitoring at different places of the Earth surface. Many results have been reported during the 1990 s where data from the ERS-1 and ERS-2 SAR sensors were used. This paper will present the ongoing long-term subsidence project in Norway, AO-1104, that are making use of...

During the period 1973–1999, the effects of air pollution on the terrestrial ecosystems in the border areas of Norway and Russia have been investigated by the use of satellite remote sensing. Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM) data, in combination with field work data collected in the period 1970–2000, were applied to prod...

We have investigated whether synthetic aperture radar images can be used to observe and position the fish farms and polymer type fish cages along the Norwegian coast. In order to maximize sea-object backscatter difference, the images selected are Radarsat F5 with 10 m×10 m resolution, 45-48° incidence angle and HH-polarization. We found that it was...

Digital elevation model (DEM) generation has mainly been based on optical imagery and photogrammetric techniques. However, in recent years there has been a growing interest in the use of synthetic aperture radar (SAR) for this purpose. It is mainly two techniques that are used, SAR interferometry and stereoSAR. We have studied the influence of the...

A change in climate in northern Europe in the last decades has probably changed the timing of onset of the birch pollen season. In Denmark it is reported that from 1977 to 2000 the date on which the accumulated birch pollen counts reached 2.5 percent of the total catch has changed from 12th of May to 25th of April. The total cumulated amount of bir...

This study use the GIMMS NDVI dataset from 1981 to 1999 covering north-western Europe, and surface pollen, phenology and climatic data for the same period. By using an individual threshold NDVI value for defining the onset of the growing season applied to each pixel for each year a high correlation was found with pollen, phenology and climatic surf...

This paper describes the theoretical relation between interferometric phase and changes in snow water equivalent (SWE) and show results from experiments using ERS-&frac12; tandem data. The main scattering contribution from a dry snow cover is from the snow-ground interface. However, the radar wave will be refracted in the snow. Thus, only small cha...

The GIMMS NDVI dataset was used to investigate regional climatic change impact on the length of the growing season in Fennoscandia, Denmark and Kola Peninsula. In general, results show a pattern according to vegetation zones (mostly north-south direction) and vegetation belts (altitude), and partly according to vegetation sections (mostly east-west...

A preliminary validation of the ASAR Level 1b (cross spectra) product and the Level 2 (wave spectra retrieval) algorithm have been conducted using ERS Wave and Image Mode SLC data collocated with in-situ measurements and numerical wave model. The objectives of the validation have been to optimize the algorithms, the processing settings and to predi...

In case of dry snow, only small changes (cm) in snow depth between two images pairs significantly increases the error in DEM generation due to the disturbance of the phase property, although no effects are observed on the coherence. Thus, the degree of coherence is not a sufficient parameter for estimating the expected error in DEM generation for s...

Two new methods for estimating wind parameters from SAR image spectra is discussed and tested. Both methods apply the azimuth cut-off strongly dependent on both the large and the small scale of the ocean wave system, where only the small scale part (typical smaller than the SAR resolution) is directly connected to the wind speed. The simplest metho...

The authors have studied the significance of non-Gaussian signal statistics in some synthetic aperture radar (SAR) images of the ocean surface. The study consisted of calculating the amplitude histogram of the returned echoes from the images and comparing these with the Rayleigh- and Kν-distributions, corresponding to the Gaussian and non-Gaussian...

The need to locate areas of abnormal vegetation change arises when one wants to detect and limit areas damaged or recovering from e.g. heavy air pollution. The authors demonstrate two different methods for change detection, in order to determine the extent of vegetation change due to heavy pollution from the Cu-Ni smelters in the Monchegorsk area o...

Air pollution impact on the vegetation cover in the north-eastern region of Norway is documented using satellite remote sensing. Landsat images obtained from 1973 to 1994 are analysed. Vegetation cover maps and change detection maps are produced. One of the main changes observed is that the area with lichen heaths decreased from 30% of the investig...

Ocean spectral peaks extracted from synthetic aperture radar (SAR) imagery exhibit a wavenumber rotation and shift relative to the true peaks due to attenuation of the high azimuth wavenumbers. We develop an approximate analytical model allowing a correction to the rotation and shift of SAR spectral peaks. This model maybe useful for spectral peak...

Ocean spectral peaks extracted from synthetic aperture radar (SAR) imagery exhibit a wavenumber rotation and shift relative to the true peaks due to attenuation of the high azimuth wavenumbers. We develop an approximate analytical model allowing a correction to the rotation and shift of SAR spectral peaks. This model maybe useful for spectral peak...

The phase and amplitude of the real aperture radar (RAR) modulation transfer function (MTF) are, applying both simulated and real synthetic aperture radar (SAR) image spectra, shown to strongly influence the SAR ocean wave imaging of range- (or near-range) traveling wave systems. This paper proposes a new method for estimating the RAR MTF directly...

A new method for estimating the phase and amplitude of the real aperture radar (RAR) modulation transfer function (MTF) is proposed. Conventionally, in situ measurements of the seastate have been used in connection with SAR estimation of the RAR MTF. However, investigations using synthetic data reveal that the SAR image spectrum for realistic seast...

Describes the project to assess the potential of SAR data for snow cover monitoring. The project is a joint project between NORUT IT and SINTEF-NHL. The authors have acquired 16 ERS-1 SAR data sets and conducted four field measurements from a test area in Norway in the snow melt period of 1992. The preliminary results shows that the C-band SAR is c...

The well-known along-track resolution loss in synthetic aperture radar (SAR) ocean wave image spectra is investigated comparing simulations based on Hasselmann's nonlinear integral transform and measurements from the Norwegian Continental Shelf Experiment 1988 experiment. In the literature the resolution loss has often been modeled as a low-pass fi...

Results from validating the ocean wave spectra derived from ERS-1 SAR image mode data are presented. The wave spectra are obtained by combining numerical wave model data with SAR data in an inversion process. The validation is performed using in-situ reference data provided by directional and non-directional wave buoys. A variety of sea-states are...

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