Intercomparison of Integrated Water Vapor Measurements at High Latitudes from Co-Located and Near-Located Instruments

Ermanno Fionda,Vinia Mattioli,Rosa Pacione,Maria Cadeddu

doi:10.3390/rs11182130

Ermanno Fionda, Vinia Mattioli + Show 2 more

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https://doi.org/10.3390/rs11182130

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Abstract

Data from global positioning system (GPS) ground-based receivers, ground-based microwave radiometers (MWRs), and radiosondes (RS) at two high-latitude sites were compared. At one site, the North Slope of Alaska (NSA), Barrow, Alaska (USA), the instruments were co-located, while at the other site, the second ARM Mobile Facility (AMF2), Hyytiälä, Finland, the GPS receiver was located about 20 km away from the MWRs and RS. Differences between the GPS-derived integrated water vapor (IWV) and the other three instruments were analyzed in terms of mean differences and standard deviation. A comparison of co-located and near-located independently calibrated instruments allowed us to isolate issues that may be specific to a single system and, to some extent, to isolate the effects of the distance between the GPS receiver and the remaining instruments. The results showed that at these two high-latitude sites, when the IWV was less than 15 kg/m2, the GPS agreed with other instruments within 0.5–0.7 kg/m2. When the variability of water vapor was higher, mostly in the summer months, the GPS agreed with other instruments within 0.8–1 kg/m2. The total random uncertainty between the GPS and the other systems was of the order of 0.6–1 kg/m2 and was the dominant effect when the IWV was higher than 15 kg/m2.

Highlights

Water vapor accounts for only about 0.25% of the total mass of the atmosphere, it determines most of the earth’s energy budget and large-scale circulation [1]
Global positioning system (GPS) observations are of high relevance, and there has been a fast growth of ground network receivers, making global positioning system (GPS) crucial for water vapor monitoring
The estimate of integrated water vapor (IWV) from a GPS is possible thanks to the linear relationship between the zenith wet delay (ZWD) and the IWV present in the volume of atmosphere traversed by the signal from space to the ground receiver

Summary

Introduction

Water vapor accounts for only about 0.25% of the total mass of the atmosphere, it determines most of the earth’s energy budget and large-scale circulation [1]. Since about 1930, regular observations of moisture profiles have been possible thanks to the radiosonde (RS), and today a variety of instruments monitor water vapor at various temporal and spatial scales. Among these techniques, global positioning system (GPS) observations are of high relevance, and there has been a fast growth of ground network receivers (arranged into regional or global networks), making GPS crucial for water vapor monitoring. From a statistical point of view, intercomparison analyses have highlighted discrepancies in terms of systematic errors (bias) and random errors (standard deviation, SD) These discrepancies can be attributed to climatic conditions, the length of observations, and characteristics of the instruments such as instrumental errors, the volume sampled, sensitivity, and the sampling time as well as to water vapor retrieval algorithms

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