Shipboard meteorological sensor comparison: ICEALOT 2008

Meteorological Measurements made from ships are always challenging not only because of the marine environment, but because there are so many different types of instrumentation to chose from. Having a reliable set of standard instruments for the basic measurements of temperature, relative humidity, pressure, winds, precipitation, and incoming radiation (long and short-wave) was the main purpose of the Improved Meteorological (IMET) system (Hosom et al., 1995) currently in use on most NOAA and Woods Hole Oceanographic Institute research vessels. It is only logical as technology improves to consider changes to these instruments therefore increasing their reliability and accuracy. Another consideration is the need for higher temporal resolution to help improve model parameterization (Fairall and Bradley, 2006, Fairall et al., 2008). It is critical to conduct real-world inter-comparisons before making any changes. These comparisons provide a smooth transition between sensors and an understanding not only the accuracies, but of their operating characteristics in the often harsh marine environment.

This paper shows results from instrument comparisons during the International Chemical Experiment in the Arctic Lower Troposphere (ICEALOT 2008) using three different sets of meteorological sensors: the Improved Meteorological (IMET) system, the Vaisala Weather Transmitter WXT510 (WXT), and the Physical Science Division Flux Standard (FLUX). The research cruise was broken up into two legs. The first leg started March 19, 2008 just north of Boston, MA crossing the North Atlantic to the coast of Norway ending with a short stop in Tromso, Norway April 12, 2008. The second leg continued north towards the ice pack, reaching 80o N before heading south as close to the Greenland coast as ice conditions would allow arriving in Reykjavik, Iceland April 23, 2008.

All three sets of sensors were mounted on the forward mast of the Research Vessel Knorr. Some of the major differences between these three systems are the how the winds and precipitation are measured. For the winds, IMET uses a prop-vane while the WXT510 is a 2-axis sonic anemometer and the FLUX a 3-axis sonic anemometer: mechanical (propeller-vane) versus acoustic sampling (sonics). For precipitation, IMET is a self-siphoning rain gauge while the WXT uses the acoustic signal intensity from falling drops with larger drops generating a larger signal, and the FLUX has an optically based sensor.

Results show that precipitation, followed by winds, provide the most challenge to inter-compare and interpret. IMET precipitation showed significantly greater accumulations during the limited number of rain events. This is in direct contradiction to results from previous tests. Relative winds show overall good agreement with slightly lower wind speeds reported on the average from the IMET propeller-vane. The WXT sonic anemometer showed a possible offset or