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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #94171
Title: DIGITIZING CHART RECORDER DATA: COORDINATE SYSTEM CONVERSION FOR RAIN GAGES AND SIMILAR RECORDING INSTRUMENTS

Author
item WALTER, M - CORNELL UNIVERSITY
item Mutch, Paul
item SALMON, C - CORNELL UNIVERSITY
item McCool, Donald
item HEDIN, L - CORNELL UNIVERSITY

Submitted to: Journal of Atmospheric and Ocean Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The transformation methodology presented in this paper allows for quick, easy, and accurate distillation of chart recorder data. No complicated or obscure software or hardware are required. In a comparison of six charts representing a variety of precipitation regimes and chart scales, method was at least as adequate, and in many ways much better than the traditional, manual tabulation approach. While advances in the technology of data collection may someday make chart-recorders obsolete, they are currently used throughout the world for a wide range of measurements. Also, because chart recorder data are usually the best source of continuous data for historical records, methods, like the one presented in this manuscript, for rapidly and accurately extracting such information will continue to be valuable for many years.

Technical Abstract: Though chart recorder data is widely available for many environmental parameters over long periods of record, the non-orthogonal coordinate systems of many types of recorder charts complicates data extraction such that it is almost always manual: a tedious chore involving hand-counting tiny red boxes. Perhaps the most common data available on these types of charts are precipitation from weighing-type recording rain gages. Unfortunately, because most digitizer software assumes the data being digitized have an orthogonal coordinate system, the non-orthoganality inherent in these charts prevents simple digitization of the data. If methodologies exist for electronically extracting rain gage data, they are not widely known; recent texts like the Manual on Watershed Instrumentation and Measurements (Ffolliott, 1990) still outline manual break-point tabulation in detail, with no reference to any software or published methodologies for electronic data extraction. A simple procedure is presented here to transform digitized chart recorder data into meaningful, accurate data using readily available software. A comparison of manually read precipitation data and precipitation data extracted with a digitizer showed average differences of less than half the smallest marked increment on the charts for both precipitation amount and time. Differences were almost exclusively due to human bias in locating break-points rather than true error.