An Architecture for Monitoring Humidity Using Cellular Network Signals

The distribution of near-surface humidity is critical in forecasting convective initiation, severe storm development and intensification. Although dense observing networks such as Oklahoma’s Mesonet (McPherson et al., 2007) can define this distribution with appropriate temporal and spatial resolution, such networks currently exist only in a few states and would be infeasible to deploy in remote areas or complex terrain. In this paper, we demonstrate methods for passively retrieving near-surface humidity by monitoring the amplitude and phase of signals broadcast from cellular network base-stations. Deployment of low-cost signal monitoring stations could in the future provide regional- or national-scale near-surface humidity fields for assimilation into high resolution NWP. The methods are applicable to current wireless broadcast bands (below 6 GHz) and will be extensible to future 5G cellular technology, where signals up to 28 GHz and from 37-40 GHz will provide significantly greater sensitivity for humidity measurements.

Multiple, passive monitoring stations would receive and analyze the microwave reference and synchronization signals from the cellular broadcast towers. By comparing these parameters between stations, temporal variation in the broadcast signals is removed, thereby eliminating the need to interface with the cellular network operator. The receiving stations would exploit directional antennae to control multipath, and Software Define Radio to support flexible monitoring of base stations at different frequencies and bandwidths.

In the paper we will describe cellular broadcast signal amplitude and phase measurement concepts, evaluate receiver designs and develop a monitoring station configuration concept. Its feasibility is assessed via a small-scale prototyping and demonstration effort, and appropriate follow-on efforts are described.

In parallel, Observing System Simulation Experiments (OSSE) are conducted to assess the impact of these measurements on NWP, and to explore sensitivity to the parameters of a notional network of microwave path links (density, link-length and overlap).

Reference: McPherson, R. A., C. Fiebrich, K. C. Crawford, R. L. Elliott, J. R. Kilby, D. L. Grimsley, J. E. Martinez, J. B. Basara, B. G. Illston, D. A. Morris, K. A. Kloesel, S. J. Stadler, A. D. Melvin, A.J. Sutherland, and H. Shrivastava, 2007: Statewide monitoring of the mesoscale environment: A technical update on the Oklahoma Mesonet. J. Atmos. Oceanic Tech., 24, 301–321. DOI: 10.1175/JTECH1976.1