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 = ε 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.

Morfometrične analize vrtač – problem določanja oboda in računanja osnovnih parametrov
Nezanesljivost korelacij med okoljskimi dejavniki in geometrijo vrtač je spodbudila pregled do sedaj uporabljenih metod določanja oboda vrtač in primernosti morfometričnih analiz, ki sledijo iz teh podatkov. V prispevku preverjamo zanesljivost najširše dostopnih podatkovnih virov za določanje oboda vrtač, in sicer topografskih kart v merilu 1 : 5000 in ortofotov z ločljivostjo 0,5 m. Zanesljivost smo določali na primeru Dinarskega krasa (otok Krk, SV Jadransko morje). Primernost do sedaj najpogosteje uporabljenih parametrov (tj. sploščenost in krožnost) in njunih različic, ki se pojavljajo v literaturi, smo matematično preverili in preizkusili pri realnem naboru vrtač. Simulacija delovanja posamezne metode na poligonih z naraščajočo krožnostjo in sploščenostjo je pokazala njihova območja veljavnosti. Učinkovitost metod smo nato preverili še pri realnem vzorcu vrtač, pri katerem smo ugotovili, katera je najprimernejša različica posameznega parametra (krožnost = Pcc/Pd; sploščenost = ε prilegajoče elipse), in jo, da bi zagotovili večjo usklajenost in primerljivost rezultatov, predlagali za nadaljnjo rabo v prihodnjih morfometričnih analizah vrtač. Kot dodaten parameter za analizo tlorisa vrtač smo razvili in preizkusili indeks asimetrije oboda vrtač, tj.razdaljo med težiščem tlorisa vrtače in težiščem največjega včrtanega kroga.
Ključne besede: kras, določanje oboda vrtač, morfometrične analize, merske napake, otok Krk.