The task needs the harmony of the survey and of the interpretation because good results can be obtained only 
by the complex application of the aerial photograph. 
The first trials are carried out, at the Management of South Transdanubian Water Conservancy on the laid 
down principles of this article. 
30. Poso, S. 
Finland 
GROUPWISE SAMPLING TO BE APPLIED TO THE INVENTORY OF 
NATURAL RESOURCES WITH THE AID OF PHOTO INTERPRETATION 
Studies concerning the applicability of photo interpretation to the inventory of natural resources focus on two 
points: 1) how precise the photo interpretation is in respect of various items subject to inventory, and 2) which 
method is most suitable for the application of the photo interpretation. This study deals with the latter problem. 
The results and suggestion are based on studies made in Finland in the field of forest inventory. Most of the 
findings may be regarded as directly adaptable also to other resource inventories. 
A uniform grid of points is laid out on the photographs. The points are supplied with coordinates determining 
the exact geographical location. All the points are grouped into as homogeneous groups as possible in respect 
to all important characteristics subject to inventory. From each group only one point will be selected to be 
measured in the field. The results based on field measurements are then expanded to cover all the points 
belonging to the respective groups. Such a procedure results in formally complete data for each photo 
interpreted point. This makes the computations easy for any desired sub-district or other class than can be 
defined on the basis of the field-corrected characteristics of the photo points. Also, the efficiency of this method 
can be expected to be better than that of ordinary methods based on double sampling. 
31. Ridai, O. 
Hungary 
THERMAL INVESTIGATIONS IN HUNGARY 
Hungary, with its surface of 93,000 m^ occupies the central part of the Karpathian Basin. The reciprocal 
geothermal gradient differs here from the average; being equal to about 20 m/C 
According to geophysical soundings, it is caused by the relatively thin crust of the region. The **geotumor", 
or medial mass, encircled by the arch of the Karpaths is an unstable area; this shown by the recent, although 
relatively rare, earthquakes and tectonic movements along structural line. 
The natural thermal springs and thermal wells are of course in close connection with the factors mentioned 
above. Subsurface water has a great importance in the Hungarian water-management, even if it is not warm. 
Some natural thermal springs do pour into the rivers, thus remaining hidden under the surface of the river. 
The thermal investigations with thermovision had already begun. The most interesting result is the exploration 
of some new spots of thermal spring activity in the river Danube. 
The pumping of karstwater from the coal mines disturbed the natural water balance of several regions, thus 
threatening the thermal springs. If the depression of the influenced area does reach to the springs it is possible 
that the former springs will turn into swallow-holes; then the thermograms would have enormous 
importance. 
The next investigations will show the possibilities of the detection of dam leakage, important for flood 
control. 
Infrared photography and infrared imagery would be of great interest not only in the above mentioned cases, 
but also for the investigation of thermal anomalies which are possible new sites of thermal water 
exploration. 
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