Evaluating the Applicability of Thermal Infrared Remote Sensing in Estimating Water Potential of the Karst Aquifer: A Case Study in North Adriatic, Croatia

Bojana Horvat,Josip Rubinić

doi:10.3390/rs13183737

Abstract

One of the most prominent tourist destinations in the Adriatic coast, the city of Opatija, is facing a problem concerning seasonal drinking water shortages. The existing water resources are no longer sufficient, and attention is being given to alternative resources such as the underlying karstic aquifer and several coastal springs in the city itself. However, the water potential of the area still cannot be estimated due to the insufficient hydrological data. The goal of this research was to evaluate the use of thermal infrared (TIR) remote sensing as the source of valuable information that will improve our understanding of the groundwater discharge dynamics. Ten Landsat ETM+ (enhanced thematic mapper plus) and two Landsat TM (thematic mapper) images of the north Adriatic, recorded during 1999–2004 at the same time as the field discharge measurements, were used to derive sea surface temperature (SST) and to analyze freshwater outflows seen as the thermal anomaly in the TIR images. The approach is based on finding the functional relationship between the size of the freshwater thermal signatures and the measured discharge data, and to estimate the water potential of the underlying aquifer. It also involved analyzing the possible connection between the adjusted size of the spring’s thermal signatures and groundwater level fluctuations in the deeper karst hinterland. The proposed methodology resulted in realistic discharge estimates, as well as a good fit between thermal anomalies with measured discharges and the groundwater level. It should be emphasized that the results are site specific and based on a limited data set. However, they confirm that the proposed method can provide additional information on groundwater outflow dynamics and coastal springs’ freshwater quantification.

Highlights

The increase in frequency and intensity of extreme hydrological events over the past few decades has emphasized the lack of freshwater availability throughout the world [1,2,3,4]
sea surface temperature (SST) maps were created for each Landsat image (Figure 2)
Twelve images showing the spatial distribution of SST indicate variation of the SST depending on the season

Summary

Introduction

The increase in frequency and intensity of extreme hydrological events (e.g., droughts as well as floods) over the past few decades has emphasized the lack of freshwater availability throughout the world [1,2,3,4]. Investigations conducted over the last decades emphasized the importance of coastal and submarine springs worldwide (e.g., [5,6,7,8,9]), in terms of their availability to meet the freshwater demand and for their importance for the coastal ecology. Coastal and submarine springs are common along the Mediterranean coastline [10], including the Adriatic Sea (e.g., [11]). Discharge processes of the coastal and submarine springs are complex. Assessing the discharged quantities by means of direct measurements is often not possible, so finding an adequate approach to estimate water availability in dynamic contact conditions between fresh water and sea water is a challenging task. Various methods have been proposed to quantify coastal and submarine springs including techniques based on the Remote Sens.

Objectives

Results

Conclusion