ASTRA - Atmospheric & Space Technology Research Associates, LLC

Validation of Cases Performance In Scintillating Environments

 

During the final stages of development, a CASES receiver was deployed at the Jicamarca Radar Observatory (JRO) in Peru, where instabilities which lead to scintillation such as Equatorial Spread-F are frequently observed. The receiver was located at JRO for a year and a half, and was operated remotely from Boulder, CO, USA for the entirety of its stay. During this time, it consistently observed TEC fluctuations (see Fig below) and ionospheric scintillation.

In addition, the CASES development team was given the opportunity to test the receiver’s performance in severely scintillating environments against competing commercial GPS space weather monitors.

The competing commercial scintillation monitor consistently lost lock during the deepest power fades, while CASES was able to observe fades as deep as -45 dB while still maintaining lock on the signal. The figure below compares the performance of the CASES receiver (blue curve) with a co-located competing receiver (red curve) near Lima, Peru during severe scintillation [O’Hanlon et al, 2012].  CASES was able to track through the severe scintillation with {S4, tau-0, amplitude} combinations as large as {0.8, 0.8 seconds, 43 dB-Hz (nominal)}, commensurate with vigorous post-sunset equatorial scintillation, with a mean time between cycle slips greater than 450 seconds and with a mean time between frequency-unlock greater than 1 hour. In contrast, the competing receiver lost lock many times per minute. The CASES performance greatly exceeds other units on the market, and means CASES receivers can be used in challenging environments, or to accurately monitor challenging environments such as scintillation conditions. The CASES receiver appears to outperform other receivers that have previously been considered the ‘gold-standard’ for scintillation measurement and monitoring, while CASES is also considerably less expensive, and can be remotely reconfigured.

Figure 7. The CASES specialized tracking loop (blue trace) allows robust tracking during scintillations versus competing receivers that use fixed bandwidth PLL (red trace) which lose lock. Data collected from Jicamarca, Peru at magnetic equator by Brady O’Hanlon.

Another comparison between CASES and a competing receiver was carried out at South Pole, Antarctica [Deshpande et al, 2012]. The figure below compares the phase variations measured by the two receivers during a mild phase-scintillation event. The top panel shows the CASES data, and the lower panel shows data from the competing  receiver. The results are basically identical in this case. The CASES receiver at South Pole is buried in the snow outside of Scott Base, with limited resources as it relies on solar panels. Therefore it buffers data and is programmed to only save data to disk during scintillation events. The scintillation shown in the figure triggered the receiver to save the data from 200 seconds earlier, so that the evolution of the scintillation event could be studied. In contrast, the competing receiver is housed inside Scott Base, where power is essentially unlimited.

Figure 9: depicts 3000 seconds of data from the CASES receiver, and illustrates the increase of S4 (upper panel) during a time of varying C/N0 (lower panel), showing that CASES is extremely sensitive and has a low threshold for scintillation. (Figure courtesy, T. Humphries, UTAustin).