Eugenio Zilioli

DETECTING CHLOROPHYLL, SECCHI DISK DEPTH AND SURFACE TEMPERATURE IN A SUB-ALPINE LAKE USING LANDSAT IMAGERY

Some bio-physical parameters, such as chlorophyll a concentration, Secchi disk depth and water surface temperature were mapped in the sub-alpine Lake Iseo (Italy) using Landsat Thematic Mapper (TM) data acquired on the 7 March 1997. In order to adequately investigate the water-leaving radiance, TM data were atmospherically corrected using a partially image-based method, and the atmospheric transmittance was measured in synchrony with the satellite passage. An empirical approach of relating atmospherically corrected TM spectral reflectance values to in situ measurements, collected during the satellite data acquisition, was used. The models developed were used to map the chlorophyll concentration and Secchi disk depth throughout the lake. Both models gave high determination coefficients (R2 = 0.99 for chlorophyll and R2 = 0.85 for the Secchi disk) and the spatial distribution of chlorophyll concentration and Secchi disk depth was mapped with contour intervals of 1 mg/m3 and 1 m, respectively. A scene-independent procedure was used to derive the surface temperature of the lake from the TM data with a root mean square error of 0.3 degrees C.

Determination of chlorophyll concentration changes in Lake Garda using an image-based radiative transfer code for Landsat TM images

The distribution of phytoplankton chlorophyll concentration in Lake Garda (Italy) was estimated using Landsat Thematic Mapper (TM) data acquired at two different times, February 1992 and March 1993. To investigate the waterleaving radiance adequately, the contribution of the atmospheric path radiance reaching the sensor should be removed. In this work a completely image-based atmospheric correction method was applied by means of an inversion technique based on a simplified radiative transfer code (RTC). A semi-empirical approach of relating atmospherically corrected TM spectral reflectances to in situ measurements through regression analysis was used. Limnological parameters were measured near to the TM images dates; some of the in situ measurements were used to define algorithms relating chlorophyll concentration measurements to water surface reflectance and the others too were used to validate the results of the predictive model. The models developed, which performed better (r2 = 0.818) when concentrations were higher than > 3.0 mg m3, were used to map chlorophyll concentration throughout the lake. Spatial distribution maps of chlorophyll concentration and concentration changes were produced with contour intervals of 1 mg m3.

The satellite derived optical information for the comparative assessment of lacustrine water quality

Abstract The objective of this research is to define the support that can be derived from satellite optical remote sensing to monitor the trophic status of lake waters, even in the absence of corroborating in situ measurements. An analysis was conducted on Lake Garda (Italy), where sub-basins showing different water quality conditions can be delineated. For this purpose, two Landsat-TM images, taken in April and August 1985, at specific seasonal situations of the limnological cycle were used. Image processing provided radiance-derived quantities, such as reflectance and chromaticity, in the form of digital transects drawn from the margin of the lake to cross the pelagic environment. In order to make the multi-temporal analysis possible, a method for compensating the differential haze effect between the two images, based on the darkest object technique was adopted. Results demonstrated the suitability of satellite remote sensing observations as a fast and relatively low cost effective tool for early and expeditious assessment of both the spatial and temporal variability of lake water quality conditions.

Validation of satellite data for quality assurance in lake monitoring applications

The operational application of remote sensing technologies to lake water quality monitoring requires products derived from remote sensing to be quantitatively self-consistent and have a certified accuracy. Fundamental elements in this quality assurance framework are sensor radiometric calibration and atmospheric correction models, which are briefly discussed in the paper. In order to evaluate the accuracy of present operational techniques to retrieve basic parameters from satellite data, such as water-leaving radiance and reflectance, an experiment was organised in the frame of SAtellite remote sensing for Lake MONitoring (SALMON), a European Union co-funded research project. A series of ship-based radiometric and atmospheric measuring campaigns were conducted on Lake Iseo and Lake Garda (Italy) together with limnological sampling. Four Landsat-5 Thematic Mapper (TM) scenes were acquired during different seasons and simultaneous in situ measurements were made. After the radiometric calibration procedure, satellite digital images were processed by applying two entirely image-based atmospheric correction models. These models account for the effects of both additive scattering and multiplicative transmittance effects in the atmosphere on the at-satellite measured signal. The results achieved using these procedures were evaluated by comparing satellite-based estimates with in situ measurements of water reflectance. The root mean square difference between Landsat TM-derived reflectance values and ground measurements was close to 0.010 reflectance for each TM spectral band. Such image-based correction models, requiring no in situ field measurements during the satellite overpass, constitute a valid method of lake water monitoring.

A hybrid approach to fuzzy land cover mapping

Abstract We propose here a fuzzy hybrid methodology for the classification, conceived as a cognitive process, of remote sensing images. The salient aspect of the approach is the combined use of different techniques: the linear mixture model , a supervised fuzzy statistical classifier and a fuzzy labeling technique. An application for the identification of rice crops in a Landsat Thematic Mapper image has been developed with the aim of experimentally evaluating the performance of the overall strategy in a real domain where fuzzy membership to classes are essential in class discrimination. The results have then been compared with those obtained by means of the Maximum Likelihood classifier.

A correlation between optical properties from satellite data and some indicators of eutrophication in Lake Garda (Italy)

Abstract Here we present the first results of a research project in the field of optical remote sensing from a satellite platform to monitor the lacustrine environment. Landsat Thematic Mapper imagery was considered, on the basis of good performances in the visible bands, which is particularly useful for studies of water quality. The study involves Lake Garda (Italy) and concerns the correlation between remote sensing observations of the surface characteristics of water bodies and the eutrophication trend, as derived from bottom sediment cores. Image processing provided radiance-derived quantities, by means of transects, from the shoreline to the pelagic environment, in two separate sub-basins marked by different eutrophication. A correlation between the recent and present eutrophication trends and the optical properties of the water, as seen by remote sensing, was observed. This approach can be seen as a new remote sensing application to the study of lacustrine environments, since it permitted a comparison of instantaneous information, taken from a space platform, with a long-term data set obtained from sediments deposited at the bottom of the lake.

Thermal inertia of rocks—an HCMM experiment on Sardinia, Italy†

Abstract The usefulness of thermal inertia mapping for discriminating litholog-ical units was investigated using Sardinia and the Gulf of Orosei as test sites. Software designed forXANDSAT data was modified and improved for HCMM tapes. A first attempt was made to compare the geological cross-section, the topography, the infrared radiance and the thermal inertia along selected profiles of the test site. Thermal inertia profiles appear smooth in comparison with the thermal radiance. The lowest apparent thermal inertia (ATI) was found on granitic and basaltic outcrops of sufficient extent, while ATI is higher on carbonate and dolomitic or moist deposits, Almost every fault is marked by a jump in the ATI, the interval being sometimes of the order of I pixel. This seems to demonstrate the ability of ATI to detect contacts or tectonically disturbed zones with good resolution. It seems more difficult to measure the differences in ATI between homogeneous materials having different lithology. The results of ground...

Subpixel estimation of the Venice lagoon wetlands using Thematic Mapper data

This paper deals with the application of a modified linear mixture model (MLM) to the satellite image classification for a precise evaluation of the landscape unit surfaces in the lagoon environments where transitional zones between continent and sea waters are marked by clusters of mixed pixels. The importance of a precise classification for these border-pixels is evident since satellite observations could become a very precious tool in the monitoring of erosion/sedimentation rate of wetlands. The study area is located in the lagoon of Venice (Italy) which has been subjected to a slow but continuous sinking since the beginning of this century causing a remarkable loss in the extension of wetlands. A data set of three Landsat Thematic Mapper passages was used, 3-year intervalled one another, and covering the period from 1984 to 1990. Validation of the adopted methodology was made by the support of aerial color photos, taken the same days of the 1987 satellite overflight.

Comparison of satellite and Airborne Thematic Mapper data for estimating inland water quality

The aim of this study was to compare satellite Landsat-5 Thematic Mapper (TM) data with Airborne Thematic Mapper (ATM) data, for the detection of the trophic status of water masses. Study area is the Lake Iseo, one of the most important freshwater basin in northern Italy, located in the sub-alpine ecoregion. In accordance with the Organisation for Economic Cooperation and Development (OECD) the Iseo waters are defined as meso-eutrophic. Airborne Daedalus ATM AADS-1268 data were acquired on 14th July 1992 and Landsat-5 TM data on 1st September 1992. Multi-temporal comparison required adjustment of scene radiance due to atmospheric variations. To achieve this an integrally image-based method was employed. Airborne and satellite data were used to estimate turbidity, chlorophyll and suspended sediment load, by means of chromaticity analysis. Processing of thermal images for lake surface temperature determination was also addressed. The results confirmed previous knowledge on the trophic state of Lake Iseo, in agreement with traditional investigations. Remotely data were able to separate chromaticity of the waters, discriminating different turbidity patterns distribution and emphasizing the behavior of shallower waters infected by macrophytes.

Multilevel approach to the geomorphological setting of an alluvial plain in the Alpine environment

This paper presents an integrated use of cartography and remote sensing imagery supplied by satellite and aircraft to study the geomorphological aspects of an alluvial plain for archaeological purposes. The study area is located at the confluence of the Valtellina (Adda River) and Lower Mera River valleys in northern Italy. Landsat data and aerial photographs were used to study the partial filling of the Lake Como lacustrine basin resulting from the progradation of the Adda River delta. Different soil humidity content, related to variable grain size of the alluvial deposits is an indicator of ancient river beds which were formed in this area before the nineteenth century artificial rectification of the River Addas final stretch. Profiles coincident with geological sections gained by geophysical sounding were performed on the remote sensing imagery to verify eventual correspondence of depositional features with different analysis techniques. The integration of remote sensing multilevel data with cartography and archaeological evidences has been useful for the assessment of the paleoenvironment which conditioned human settlements.