Abstract

Developments and Applications of Digital Barometers for Mariners

David Burch, PhD, Director

Starpath School of Navigation, Seattle, WA www.starpath.com

Maritime versions of traditional aneroid barometers commonly in use on vessels of all sizes and purposes are not well suited for finding absolute pressures (Note 1). They are not provided with calibration curves and most are non-linear over atmospheric pressures. In the past, however, absolute pressures were not called for. Mariners relied mostly on trends, not absolute values, to make or evaluate forecasts. (The exception, of course, are VOS participants, but these mariners have the professional assistance of PMOs to help with instrument quality and calibration issues.)

New developments in digital barometers are in the process of dramatically changing this situation by providing low-cost devices that are linear and reproducible to within about 1 mb over the full range of atmospheric pressures. They come just in time to meet a newly emerging practical need for mariners to know absolute pressures as a means of evaluating weather maps—especially model output maps ("GRIB data") that are so readily available underway these days.

With accurate pressure, wind speed, and wind direction, the mariner can evaluate the latest issue of a map based on recorded observations, and make subsequent decisions accordingly. Online sources of archived pressures make it easy to adjust individual barometers to accurate local sea level pressure.

Specific applications and specific devices are discussed and on display.

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Note1, added after the talk: The exceptions in the aneroids are the classic top of the line models such as Belfort, Airflo, Yanagi, and Fischer. These few instruments do indeed provide reliable pressures to within ± 0.7 mb over their full working range without the need for a separate calibration curve. The Fischer are now available in the U.S. from Starpath and other select dealers.