Ground-based measurement of gradients in the “wet” radio refractivity of air

摘要: We have used a ground-based microwave radiometer, known as water vapor to investigate the local spatial and temporal variation of wet propagation delay for site on west coast Sweden. The data were obtained from wide range azimuths elevation angles greater than 23.6-degrees (air mass 2.5). Visual inspection suggested simple ‘'cosine azimuth” variation, implying that first-order gradient model was required. This adequate short time spans up approximately 15 min, but significant variations in us we include rate terms. resulting six-parameter has proven (rms residual 1 mm) 30 min data. Assuming exponential profile refractivity gradient, estimated parameters imply average surface wet-refractivity horizontal gradients order 0.1-1 N km-1. These are larger, by 1-2 orders magnitude, determined others averaging over long (approximately 100-km) distances. result implies applications sensitive gradients, such propagation-delay models radio-interferometric geodetic studies, use meteorological widely spread stations may be inadequate. presented here is inadequate times longer about min. even if no present, because complicated stochastic like behavior atmosphere. When they can change magnitude 50% 10-15 Nevertheless, our ability fit radiometer timescales 23.6-degrees, structure atmosphere described with model. (The not limited this principle.) vectors preferred directions, which indicates prevailing three-dimensional temperature humidity fields, possibly related systematic large-scale weather systems and/or air-land-sea interaction at site.