Morphometric analyses of dolines — the problem of delineation and calculation of basic parameters

Abstract

So far reported unstable correlations between environmental settings and doline geometry require a revision of doline delineating methods and morphometric analyses that follows from such input data. We examine the reliability of the most accessible data sources for doline delineation, namely basic topographic maps at a scale of 1:5,000 and ortho-rectified aerial photographs (digital orthophotos) of 0.5 m resolution. Their reliability has been quantified in the Dinaric karst (Krk Island, NE Adriatic Sea). The adequacy of most commonly used morphometric parameters (viz. elongation and circularity) and their variations applied in previous studies are mathematically verified and practically tested. The simulation of an individual method behaviour performed on polygons with increasing circularity and elongation demonstrated their ranges of validity. The efficiency of a particular method was verified by the application to the real dataset of dolines. The optimal variation of an individual parameter (circularity = Pcc/Pd; elongation = e of the best fitting ellipse) is identified and suggested for use in order to provide uniform results and increase the comparability of future morphometric analyses. Asymmetry (the distance between the centroid of doline ground plan and the centroid of the largest inscribed circle) as an additional parameter for describing doline ground plans has been developed and is proposed for further use. Key words: karst, doline delineating, morphometric analyses, measurement errors, Krk Island. Morfometricne analize vrtac – problem dolocanja oboda in racunanja osnovnih parametrov Nezanesljivost korelacij med okoljskimi dejavniki in geometrijo vrtac je spodbudila pregled do sedaj uporabljenih metod dolocanja oboda vrtac in primernosti morfometricnih analiz, ki sledijo iz teh podatkov. V prispevku preverjamo zanesljivost najsirse dostopnih podatkovnih virov za dolocanje oboda vrtac, in sicer topografskih kart v merilu 1 : 5000 in ortofotov z locljivostjo 0,5 m. Zanesljivost smo dolocali na primeru Dinarskega krasa (otok Krk, SV Jadransko morje). Primernost do sedaj najpogosteje uporabljenih parametrov (tj. sploscenost in krožnost) in njunih razlicic, ki se pojavljajo v literaturi, smo matematicno preverili in preizkusili pri realnem naboru vrtac. Simulacija delovanja posamezne metode na poligonih z narascajoco krožnostjo in sploscenostjo je pokazala njihova obmocja veljavnosti. Ucinkovitost metod smo nato preverili se pri realnem vzorcu vrtac, pri katerem smo ugotovili, katera je najprimernejsa razlicica posameznega parametra (krožnost = Pcc/Pd; sploscenost = e prilegajoce elipse), in jo, da bi zagotovili vecjo usklajenost in primerljivost rezultatov, predlagali za nadaljnjo rabo v prihodnjih morfometricnih analizah vrtac. Kot dodaten parameter za analizo tlorisa vrtac smo razvili in preizkusili indeks asimetrije oboda vrtac, tj.razdaljo med težiscem tlorisa vrtace in težiscem najvecjega vcrtanega kroga. Kljucne besede: kras, dolocanje oboda vrtac, morfometricne analize, merske napake, otok Krk.