Glacier Mass Balance and Regime: Data of Measurements and ...

Golubev and Dyurgerov, 1976). Here errors recognized by value as well, including: a) gross (egregious)errors, usually large and obvious, which need to be identified and the observation eliminated, e.g.,incorrect methodology, mistake in transcription etc.; b) errors or uncertainties that can be treatedstatistically: random errors (e.g. measurement error), or systematic errors (e.g. bias in methodology).Application of this theory to measurements of glacier regime shows the primary importance ofsystematic errors, for every class. The main sources of gross errors are in connection with field work inbad weather and difficult environmental conditions, such as low temperature and atmospheric pressure,wind, snow fall, snow avalanches and so on (external errors). Additional error may be derived during theinstallment of equipment, measuring snow in pits, and probing deep and dense snow frequently (∅stremand Haakensen, 1999; Jansson, 1999). Only experienced field workers and data collectors mayrecognize such errors, take the necessary precautions, and make corrections immediately after the surveyis done. Any change of field personal may introduce new errors. This is very subjective matter and it isdifficult to apply reasonable criteria to reduce such errors. Measurement values exceeding 3 standarddeviation from a mean or expected value have been rejected in an earlier work (Golubev and Dyurgerov,1976).∅strem and Brugman (1991) conclude that any practical method of measurement in the fieldmust include intuitive as well as statistical methodologies. The intuitive skill is obtained only by muchexperience with the glaciers being measured.The sources and magnitude of errors may be affected by climate conditions, surface topography,glacier size, and inaccessibility of glacier area for measurements (avalanches, crevasses). A combinationof these factors provides a reasonable answer as to why there is no appropriate consensus scheme toestimate the entire range of errors in glacier mass balance studies.2.2.3. Estimate of accuracy and variability in glacier mass balanceTo determine accuracy in mass balance components, the following is commonly applied:σ F= [(∂F/∂x) 2 σ x2+ (∂F/∂y) 2 σ y2+ …, (∂F/∂u) 2 σ u2)] 1/2 . (4)σ Fis the square-root error of function F and is assumed to be a measure of random error of uncorrelatedvariables x, y,…u. Application this to equations (1, 2) gives an estimate of the error of mass balance andseasonal components data at any single site i:2σb i= [(ρ i2σ •h2+ ∆h i2σ ρ )] 1/2 , (5)or in relative values,32