Maciej Bartold

Monitoring Wetlands Ecosystems Using ALOS PALSAR (L-Band, HV) Supplemented by Optical Data: A Case Study of Biebrza Wetlands in Northeast Poland

The aim of the study was to elaborate the remote sensing methods for monitoring wetlands ecosystems. The investigation was carried out during the years 2002–2010 in the Biebrza Wetlands. The meteorological conditions at the test site varied from extremely dry to very wet. The authors propose applying satellite remote sensing data acquired in the optical and microwave spectrums to classify wetlands vegetation habitats for the assessment of vegetation changes and estimation of wetlands’ biophysical properties to improve monitoring of these unique, very often physically impenetrable, areas. The backscattering coefficients (σ°) calculated from ALOS PALSAR FBD (Advanced Land Observing Satellite, Phased Array type L-band Synthetic Aperture Radar, Fine Beam Dual Mode) images registered at cross polarization HV on 12 May 2008 were used to classify the main wetland communities using ground truth observations and the visual interpretation method. As a result, the σ° values were distributed among the six wetlands’ vegetation classes: scrubs, sedges-scrubs, sedges, reeds, sedges-reeds, rushes, and the areas of each community and changes were assessed. Also, the change in the biophysical variable as Leaf Area Index (LAI) is described using the information from PALSAR data. Strong linear relationships have been found between LAI and σ° derived for particular wetland classes, which then were applied to elaborate the maps of LAI distribution. The other variables used to characterize the changing environmental conditions are: surface temperature (Ts) calculated from NOAA AVHRR (National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer) and Normalized Difference Vegetation Index (NDVI) from ENVISAT MERIS (ENVIronmental SATellite MEdium Resolution Imaging Spectrometer). Differences of almost double Ts between “dry” and “wet” years were noticed that reflect observed weather conditions. The highest values of NDVI occurred in years with a sufficient amount of precipitation with the lowest in “dry” years. NDVI values variances within the same wetlands class resulted mainly from the differences in soil moisture. The results of this study show that the satellite data from microwave and optical spectrum gave the repetitive spatial information about vegetation growth conditions and could be used for monitoring wetland ecosystems.

Monitoring forest biodiversity and the impact of climate on forest environment using high-resolution satellite images

ABSTRACT The main objectives of the research work were to determine the usefulness of Landsat and SPOT data for monitoring various forest parameters, and to assess the impact of changeable climatic conditions with the use of vegetation indices derived from remotely sensed data. Vegetation indices describing various aspects of plant condition and vegetation structure were derived from satellite images, and their values were analysed in a temporal profile in different vegetation seasons, in conjunction with meteorological parameters. The results of analyses proved that dedicated vegetation indices of water stress in plants – the disease water stress index (DSWI) and normalized difference infrared index (NDII) – are able to detect changeable climatic conditions, especially the impact of drought on forest ecosystems. The indices are also useful for characterising types of forest site and tree stand mixture, in particular differentiating dry, fresh and humid forest sites. Results of analysis of satellite-based indices were supported by conclusions drawn from a study of vegetation parameters obtained in the course of field campaigns.

Importance of grasslands monitoring applying optical and radar satellite data in perspective of changing climate

Grasslands deliver wide range of ecosystem services such as carbon sequestration, water quality, flood and erosion control as well as biomass. But since they are impacted by climate change, there is a need for their constant monitoring. Due to climate changes the following grasslands growth conditions are modified: soil moisture, biomass and as a consequence carbon balance. Required multi-temporal and spatial observations are possible with satellite data. The objective of this paper is to present the long term observations of temperature and vegetation conditions (NDVI) of grasslands on the basis of MODIS satellite data as well as already performed and further scheduled frequent analysis of carbon balance, soil moisture and biomass performed with the application of Sentinel1 A; B and Sentinel2 A&B.

Application of Sentinel-1 VH and VV and Sentinel-2 for soil moisture studies

The results of application of microwave and optical satellite data for soil moisture (SM) assessment are presented. The research has been carried out from 2015 to 2016 at Biebrza Wetlands test site located in North-East Poland, designated by Ramsar Convention as Wetlands of International Importance. A regression models based on Sentinel-1 backscattering coefficients (σ°) have been developed to generate the soil moisture (SM) maps over Biebrza Wetlands. The optical data from Sentinel-2 have been used for the classification of wetlands vegetation habitats to improve SM predictions. The wetland vegetation differed, there were reeds, sedge-moss, sedges, grass-herbs, and grass. The majority of the changes occurred in moist habitats, while anthropogenic appeared more stable during study period. The observed changes were referred to moving/grazing changes and weather effects causing droughts/floods. SM differed from 30% during the drought season in 2015 to 95% in the wet season in 2016. It has been examined the impact of biomass and SM on microwave signal under changing soil moisture and vegetation growth conditions. Vegetation biomass has been characterized by measured in-situ LAI and by vegetation indices calculated from Sentinel-2, Terra MODIS data. The impact of SM and LAI on σ° calculated from Sentinel-1 data showed that LAI dominates the influence on σ° when SM is low. The analysis have been done to estimate the threshold of the SM values which dominate the backscatter. This study demonstrates the capability of Sentinel-1/2 data to estimate SM, offering an important advantage for wetlands monitoring.

Opracowanie maski obszarów leśnych w celu monitoringu kondycji zdrowotnej lasów w Polsce na podstawie wieloletnich obserwacji satelitarnych

Abstract The work presented here aims at developing cover mask for monitoring forest health in Poland using remote sensing data. The main objective was to assess the impact of using the mask on forest condition monitoring combined with vegetation indices obtained from long-term satellite data. In this study, a new mask developed from the CORINE Land Cover 2012 (CLC2012) database is presented and its one-kilometer pixel size matched to low-resolution data derived from SPOT VEGETATION satellite registrations. For vegetation mapping, only pixels with a cover ≥ 50% of broad-leaved and mixed forests defined by CLC2012 were taken into account. The masked pixels were used to evaluate spatial variability in eight Natural-Forest Regions (NFRs). The largest coverages by masked forests were obtained in Sudetian (65.7%), Carpathian (65.9%) and Baltic (51.3%) regions. For other forest regions the coverage was observed to be around 30-50%. Time-series of the Normalized Difference Vegetation Index (NDVI) comprising SPOT VEGETATION images from 1998 until 2014 were computed and cross-comparison analyses on ≥ 50% and < 50% forest cover masks brought up frequent differences at a level higher than 0.05 NDVI in seven out of eight NFRs. An exception is the Sudetian region, where the data was highly consistent. Furthermore, the Mann-Whitney U non-parametric test revealed statistically significant differences in two regions: Baltic and Masurian-Podlasie NFR. The comparative analysis of NDVI confirmed that there is a need for additional investigation of the quality of newly developed forest mask combined with vegetation and meteorological data.

The study of multifrequency microwave satellite images for vegetation biomass and humidity of the area under Ramsar convention

Wetland ecosystems keep large amounts of organic carbon and have large influence on global climate change. Net ecosystem exchange (NEE) have been modeled by means of microwave satellite images. Assessment of biomass and soil moisture has been essential for the study to elaborate the methodology for evaluating carbon sink at the ecosystem under Ramsar Convention. Backscattering coefficient (σ̊) calculated from microwave images acquired by ENVISAT, ALOS and Sentinel-1 radar sensors was analyzed along with ground truth measurements of biomass, LAI, soil moisture (SM) and NEE carried out for vegetation classes distinguished from MERIS image. The models for NEE were developed using IS4 VV which represented vegetation biomass and IS4 HH representing SM. Application of the independent set of microwave data which were possible to gather gives a valuable opportunity to verify the accuracy in assessment of biomass and humidity based on various available sensors.

Forest condition assessment through analyzing relations between meteorological parameters describing climate changes and vegetation indices derived from low-resolution satellite data

NOAA AVHRR satellite data were applied for studying relationships between vegetation indices derived from these images and meteorological parameters describing climate changes, in order to assess forest condition. Five forests areas located in various parts of Poland located in various climatic zones, characterized by different tree species were used for this purpose. 15-years database of NOAA AVHRR images and meteorological data was utilized in this work. The conducted study revealed, that there is distinct relation between meteorological situation, described by temperature and precipitation and NDVI index derived from low resolution satellite data. This conclusion is supported with results of ground measurements and high-resolution satellite data analyzed for selected forest areas.

Study and implementation of microwave and optical data for assessment of carbon balances for wetlands under changes of biomass and humidity conditions

The results of measurements of CO2 exchange in various wetland communities were elaborated for the area of Biebrza National Park in north-eastern Poland. The research has been done within ongoing ESA-PECS and National Research Project (No N N526 160040) realized in the Institute of Geodesy and Cartography, Remote Sensing Department in Warsaw. CO2 flux measurements were performed with a static chamber method from April till September from 2010 - 2012. For each of the classified wetlands vegetation habitats the relationship between soil moisture and backscattering coefficient has been examined and the best combination of microwave variables ENVISAT ASAR (wave length, incidence angle, polarization) has been used for mapping and monitoring of soil moisture. Carbon input to an ecosystem occurs through the process of photosynthesis. The rate of photosynthesis (CO2 uptake) is referred to as gross primary production (GPP). CO2 is in turn released to the atmosphere through respiration. The difference between GPP and Reco is referred to as net ecosystem exchange (NEE). By estimating the direction of NEE, it is possible to determine whether a surface is a likely source or a sink of carbon. The NEE has been related to biomass and soil moisture which was also related to the ratio of NDVI and Ts from NOAA/AVHRR.

Preliminary results of ground reflectivity measurements using noise radar

The paper describes experimental L-band ground reflectivity measurement using noise radar demonstrator working as a scatterometer. The radar ground return is usually described with a scattering coefficient, a quantity that is independent from the scatterometer system. To calculate the coefficient in a function of incidence angle, range profile values obtained after range compression were used. In order to improve dynamic range of the measurement, antenna cross-path interference was removed using lattice filter. The ground return was measured at L band both for HH and VV polarizations of radar wave as well as for HV and VH crosspolarizations using log-periodic antennas placed at a 10 m high mast directed towards a meadow surface. In the paper the theoretical considerations, noise radar setup, measurement campaign and the results are described.