Angéla Anda

Classification into homogeneous groups using combined cluster and discriminant analysis

Abstract The classification of observations into groups is a general procedure in modern research. However, when searching for homogeneous groups the difficulty of deciding whether further division of a classification is necessary or not to obtain the desired homogeneous groups arises. The presented method, Combined cluster and discriminant analysis (CCDA), aims to facilitate this decision. CCDA consists of three main steps: (I) a basic grouping procedure; (II) a core cycle where the goodness of preconceived and random classifications is determined; and (III) an evaluation step where a decision has to be made regarding division into sub-groups. These steps of the proposed method were implemented in R in a package, under the name of ccda. To present the applicability of the method, a case study on the water quality samples of Neusiedler See is presented, in which CCDA classified the 33 original sampling locations into 17 homogeneous groups, which could provide a starting point for a later recalibration of the lakes monitoring network.

Estimation of natural water body’s evaporation based on Class A pan measurements in comparison to reference evapotranspiration

⎯ A Class A pan (C) evaporation (Ep) study was conducted at the Agrometeorological Research Station of Keszthely, in the growing season of 2016. Some of the evaporation pans were implemented with freshwater aquatic macrophytes (Myriophyllum sp., Potamogeton sp., and Najas sp.) (Ps) and sediment covered bottom (S). The applied macrophytes were the predominant species of Keszthely Bay (Balaton Lake). Reference (Eo) after Shuttleworth and reference evapotranspiration (ETo) after PenmanMonteith (FAO-56 formula) were also included for the E study. Of pre-selected four investigated variables, air temperature and air humidity impacted Ep of treated Class A pans the most. Cumulative Ep values for 2016 were 363.1, 427.7, and 461.5 mm in C, S, and Ps, respectively. There was no difference in measured cumulative Ep of Ps (461.5 mm) and computed ETo (472.1 mm) during the studied season. On the basis of a simplified water budget, E rate of Keszthely Bay increased with 16.9%, when macrophytes and sediment cover were accounted. It is equivalent to 264,000,000 m3 water in Keszthely Bay’s E estimation. Simple E approach when lake’s components, such as submerged macrophytes and sediment cover were also accounted could extend the accuracy of natural lake’s E estimation in a broader circle than earlier. Key-words: Class A pan evaporation, aquatic macrophytes, Keszthely Bay (Balaton Lake)

Correction of global and reflex radiation values measured above the Lake Balaton.

Albedo measurements have been carried out since 2007 above the Lake Balaton near Keszthely and Siofok. It turned out that a systematic offset error was superposed to both the global and the reflex radiation. The value of this systematic error was approximately constant per pyranometer within a year but on the other hand it varied from year to year and from pyranometer to pyranometer. In this paper the values of this systematic errors were determined with two different methods. The difference between the values measured at night-time and the intrinsic thermal offset error of pyranometers were examined with both methods. The base of the first method is the empirical observation, that the values measured at night-time by a global radiometer are typically negative whereas by a reflex radiometer are typically positive. The substance of the second method is utilizing the air temperature measured within 1 as well as 5 hours before the radiation measuring to +select the fully overcast nights, when the thermal offset error of the global radiometer is zero. In addition, the cases where the thermal offset error of the reflex radiometer is zero were selected on the basis of the difference between water and air temperature. When the thermal offset error is zero the measured value is equal to the systematic error. Comparing the results of the two methods showed that the systematic error of the global radiometer were determined with uncertainty of 1 Wm–2, whereas that of the reflex radiometer with uncertainty of 2 Wm–2. The calibration constants were recalculated from the values being in the calibration reports taking the systematic errors into account.