This Budapest is justly famous for its thermal springs emerging in the zone near the bank of the Danube. However, it is less known that apart from springs on the riverbank, so-called drowned springs also emerge in the bed of the Danube, whose water of considerable volume flow and heat quantity discharges into the river unused. Drowned springs are natural discharges of the Buda Thermal Karst. Their volume flow and temperature are affected by stage changes of the Danube, being in close hydrodynamical relationship with the springs. Our investigations focused on the detection and location of these drowned springs-which emerge in the Danube riverbed and are assumed to have a high volume of flow-by aerial remote sensing. We have tried to detect the underwater springs near Margaret Island with low altitude aircraft and UAV flights and modern digital thermal imagers. We were looking for a quick and economical method which we can quickly map large areas before we survey the key spots from boats.
