CASES: A Novel Low-Cost Ground-based Dual-Frequency GPS Software Receiver and Space Weather Monitor

GPS receivers can be used for monitoring space weather events such as TEC variations and scintillation. This paper describes the new GPS sensor developed by ASTRA, Cornell and UT Austin. The receiver is called "Connected Autonomous Space Environment Sensor (CASE)", and represents a revolutionary advance in dual frequency GPS space-weather monitoring. CASES is a paperback-novel-sized dual-frequency GPS software receiver with robust dual-frequency tracking performance, stand-alone capability, and complete software upgradability. The receiver tracks L1 and L2 civilian signals (specifically L1 C/A, L2 CL and L2 CM). The sensor measures and calculates TEC with a relative accuracy of a few 0.01 TECU at a cadence of up to 1 Hz (post-processing up to 100 Hz). It measures amplitude and phase at up to 100 Hz on both L1 and L2-C, for up to 14 satellites in view. It calculates the standard scintillation severity indicators S-4, tau(0), and sigma(Phi), and a new index, the Scintillation Power Ration (SPR), all at a cadence that is user defined. It is able to track through scintillation with {S4, tau(0), amplitude} combinations as severe as {0.8, 0.8 seconds, 43 dB-Hz (nominal)} (i.e., commensurate with vigorous post-sunset equatorial scintillation) with a mean time between cycle slips of 480 seconds and with a mean time between frequency-unlock greater than 1 hour. Other capabilities and options include: Various data interface solutions; In-receiver and network-wide calibration of biases, and detection and mitigation of multipath; Network-wide automated remote configuration of receivers, quality control, re-processing, archiving and redistribution of data in real-time; Software products for data-processing and visualization. CASES has been designed and developed by the ionosphere community rather than adapting a commercial receiver. The low price of the sensor means that many more instruments can be purchased on a fixed budget, which will lead to new kinds of opportunities for monitoring and scientific study, including networked applications. Other potential uses for CASES receivers include geodetic and seismic monitoring, measurement of precipitable water vapor in the troposphere at meso-scale resolution, and educational outreach.