Monika Tomaszewska

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.

Urban–Rural Contrasts in Central-Eastern European Cities Using a MODIS 4 Micron Time Series

A primary impact of urbanization on the local climate is evident in the phenomenon recognized as the Urban Heat Island (UHI) effect. This urban thermal anomaly can increase the health risks of vulnerable populations to heat waves. The surface UHI results from emittance in the longer wavelengths of the thermal infrared; however, there are also urban anomalies that are detectable from radiance in the shorter wavelengths (3–5 micron) of the Middle Infrared (MIR). Radiance in the MIR can penetrate urban haze which frequently obscures urban areas by scattering visible and near infrared radiation. We analyzed seasonal and spatial variations in MIR for three Central European cities from 2003 through 2012 using Moderate Resolution Imaging Spectrometer (MODIS) band 23 (~4 micron) to evaluate whether MIR radiance could be used to characterize heat anomalies associated with urban areas. We examined the seasonality of MIR radiance over urban areas and nearby croplands and found that the urban MIR anomalies varied due to time of year: cropland MIR could be larger than urban MIR when there was more exposed soil at planting and harvest times. Further, we compared monthly mean MIR with the Normalized Difference Vegetation Index (NDVI) to analyze contrasts between urban and rural areas. We found that the seasonal dynamic range of the MIR could exceed that of the NDVI. We explored the linkage between meteorological data and MIR radiance and found a range of responses from strong to weak dependence of MIR radiance on maximum temperature and accumulated precipitation. Our results extend the understanding of the anomalous characteristics of urban areas within a rural matrix.

Viewing Global Megacities Through MODIS

Cities are often obscured by haze and smoke when viewed in the visible and near infrared, but the longer wavelengths of the middle infrared can penetrate fine aerosol layers. We characterized variation in 4-μm radiance in and nearby eight global megacities using MODIS band 23 calibrated radiance. The seasonality of middle infrared (MIR) radiance was more pronounced at higher latitudes. Precipitation attenuated MIR radiance. The seasonality of MIR radiance from exposed soils was very similar to urban surfaces, complicating discrimination. The variety of urban surfaces across the megacities also affected the seasonality of MIR radiance. Additional data and MIR radiance with higher spatial resolution could improve and refine/detail information about MIR radiance behavior for further investigation.

4\hbox{-}\upmu \text{m}

We explored variation in 4 μm radiance in and nearby eight global megacities using MODIS band 23 calibrated radiance. We found the linkage between MIR radiance seasonality and seasonal pattern of insolation, especially stronger/pronounced at higher latitude than at tropics zones. The meteorological parameter - precipitation was identified as an impact factor of MIR radiance attenuation. Similarity of MIR radiance from desert, bare soil areas, or areas with a little of crop cover to MIR radiance from urban areas makes the distinction of cover using only MIR information even impossible during the time when insolation is the highest. Also, the seasonal variations of MIR radiance are being affected by the heterogeneity of cover as different types of building and construction materials, and urban green spaces. Conceivably, additional data and MIR radiance with higher spatial resolution improve and refine/detail information about MIR radiance behavior for further investigation.

Radiance: Effects of Time of Year, Latitude, Land Cover, and View Zenith Angle

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.

MODIS 4 µm radiance in global megacities depends on seasonality, land cover, and view zenith angle

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.