GPSL Real-time Ionospheric Scintillation Monitor Plots |
The following table lists the locations of Cornell Scintillation Monitors (SCINTMONs) and dual-frequency CASES receivers. It should be noted that many of these sites are not actually administered by Cornell personell. The S4 Index indicates the intensity of amplitude scintillation seen by each receiver. The Position Error plot shows the computed average position error in addition to the average position of the antenna. For a more detailed description of the SCINTMON receiver, please see below. |
Ithaca, New York |
Cornell CASES portal |
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Austin, Texas | UT Austin CASES portal |
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Arecibo, Puerto Rico |
S4 Index |
Position Error |
Sao Luis, Brazil |
S4 Index |
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Cuiaba, Brazil |
S4 Index |
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Sao Jose dos Campos, Brazil |
S4 Index |
SCINTMON receiver description
The SCINTMON receiver was first developed in 1995 in response to the need for a GPS receiver that could measure fast ionospheric amplitude scintillations on L-band signals in the tropics. Since then, the basic SCINTMON receiver has evolved into upgraded versions which can measure phase scintillations and operate in a Real-Time Linux environment. The receiver is composed of Zarlink GPS chip sets that perform the fast digital functions such as PRN code correlation, and software running on a PC in an open architecture environment to execute the acquisition and tracking loops. By modification of the source code running in a DOS or Linux environment, the signal amplitude is computed at 50 Hz. Typically 10 channels of the SCINTMON receiver are devoted to GPS signals, one channel is devoted to a WAAS signal, and one channel is detuned to measure noise. The first 11 channels are compared to the noise channel to compute the carrier-to-noise ratios (C/N0) and the scintillation index (S4) is computed by taking the ratio of the standard deviation of C/N0 to the mean of C/N0 over a one minute period.
Since time varying amplitudes are produced whenever GPS signals reach the antenna through multiple paths, one must be somewhat careful in interpreting the S4 index. For example, multipath from local reflectors as well as actual ionospheric scintillation can produce an increase in the S4 index. Usually, but not always, multipath signal variations occur more for low elevation satellites. For a locally static environment, these variations will repeat with a period of 24 sidereal hours so that by comparing consecutive days multipath contamination can be identified. In some cases flocks of pigeons roosting near GPS antennas have caused less periodic multipath and care must be exercised before drawing conclusions.
The SCINTMON and CASES receivers have been deployed in locations in South America, Africa, Asia, Hawaii, Puerto Rico, Alaska, and around the continental US. Currently there is a network of ~20 SCINTMON receivers operating in Brazil sponsored by the Brazilian Space Agency. By employing spaced receivers, scintillation drifts can be measured and used to infer ionospheric drifts.