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An optical method of dew estimation
Author(s) -
Duvdevani S.
Publication year - 1947
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49707331705
Subject(s) - dew , dew point , environmental science , sunrise , meteorology , precipitation , confusion , hydrology (agriculture) , atmospheric sciences , geography , geology , condensation , psychology , geotechnical engineering , psychoanalysis
Abstract Former methods of observing dew were based mostly on the direct weighing, before and after exposure of a hygroscopic material. The optical method consists in identifying the appearance of dew with one of a series of standard photographs of dew. These numbered photographs correspond to a set of dew scale numbers in which each number has been related with a certain range of dew amount, as obtained by direct weighing of Leick plates and as verified later by weighing the water collected on the dew gauge itself. The scale and the gauge have been chosen to suit dew conditions at different parts of Palestine but may be adapted to different climates with very low or very high dew precipitation. Unlike the direct weighing method, the optical method is one of estimation, and though it gives valid data for monthly and annual totals, it does not yield the amount of dew on any particular night, except as lying between certain rather wide limits. On the other hand it has the following advantages over the direct weighing methods:— (1) it is inexpensive and simple, so that it lends itself easily to general use in a network of dew stations, such as has been in existence in Palestine since May 1943; (2) evaporation does not easily affect the estimates even if allowed to proceed for some time; the dew gauge can, of course, yield daily sunrise amounts by direct weighing; (3) any possibility of confusion between dew and light rain is avoided; (4) it lends itself to adaptation to direct dew observation on plants.