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

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/m 2 , the GPS agreed with other instruments within 0.5-0.7 kg/m 2 . When the variability of water vapor was higher, mostly in the summer months, the GPS agreed with other instruments within 0.8-1 kg/m 2 . The total random uncertainty between the GPS and the other systems was of the order of 0.6-1 kg/m 2 and was the dominant effect when the IWV was higher than 15 kg/m 2 . a very-long-baseline interferometry (VLBI) radio telescope [5], and numerical weather prediction models [6][7][8]. 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.The need to monitor and improve the quantification of water vapor is also essential considering incoming next-generation 5G wireless networks. In communications systems based on 5G technology, high data capacity and low latency are achieved by moving operational frequencies toward spectral regions such as the millimeter-wave band (30-300 GHz). From a communications point of view, for planning outdoor millimeter/submillimeter communication networks, water vapor is a source of signal degradations. To improve propagation models and experimental capability in the estimation of water vapor [9,10], accurate investigations of water vapor uncertainties in different climatic scenarios are desirable. However, even more importantly, since the critical 23.8-GHz water vapor frequency is so close to the 5G 24-GHz band, there is a high risk of interference, which impacts the ability to detect water vapor in the atmosphere accurately [11].In this work, we specifically focus on IWV high-latitude observations, as their retrieval remains an important challenge in this climatic regime: for example, satellite retrievals suffer from high surface reflectivity and low solar zenith angle [12]. IWV from GPSes ...

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