WBMOD

The effects of small-scale plasma density irregularities on transionospheric radio signals are a problem for a wide range of military and civilian users. The WBMOD ionospheric scintillation model was developed in order to provide a single consistent framework for (1) modeling the climatology of the irregularities which cause scintillation, and (2) calculating the effects these irregularities will have on a user-specified system. WBMOD is a hybrid model: a semi-empirical model describing the climatology of the irregularities coupled with a theoretical model for calculating the expected scintillation effects. The term “semi-empirical” is used here to underscore that while the climatology is largely a mathematical framework which has been adjusted to fit a large collection of scintillation measurements, the form of that framework and the independent variables selected for that framework were derived from an understanding of the physics underlying the generation of the irregularities.The WBMOD program uses a collection of empirically derived models to describe the global distribution and behavior of naturally occurring ionospheric irregularities, and a power law phase screen propagation model to calculate estimates of the level of intensity and phase scintillation that these irregularities would impose on a user-defined system and geometry. The outputs of the model are estimates of intensity and phase scintillation levels and occurrence statistics for the user-specified scenario.

WBMOD release (source code) is controlled by U. S. Government import/export regulation.

There are three categories of inputs to WBMOD: (1) environment state variables, (2) system definition variables, and (3) model control variables.

(1) Environment State Variable Inputs: Sunspot number, Kp, location (latitude and longitude), day of the year, and time of day

(2) System Definition Variables: System frequency (There is a low-frequency cut-off at 100 MHz, no high-frequency limit, but at frequencies exceeding 5 GHz there are impacts from hydrometeors in the lower atmosphere that begin to have an increasing impact on the signal. WBMOD does not deal with that phenomenology), phase stability time

(3) Model control variables: Satellite velocity (vx, vy, vz m/s), satellite altitude, azimuth angle step, elevation angle, grid definition file, end of link (receiver or transmitter), percentile

1. CkL : The height-integrated electron-density irregularity power-density spectrum strength at a scale-size of one kilometer (units (el2/m5)/(rad/m)3). The integration is vertically through the entire ionosphere.
2. log(CkL) : Base-10 log of CkL.
3. Integrated Density Variance (IDV) : The height-integrated electron-density variance for scale-sizes smaller than 20 kilometers (el2/m5). The integration is vertically through the entire ionosphere. The calculation of IDV (from the CkL parameter) assumes that the relative density variation through the layer, defined by ΔNe/Ne, is constant throughout the layer.
4. log(IDV) : Base-10 log of IDV.
5. S4 Index : Intensity scintillation index, defined as the intensity variance normalized to the mean intensity (dimensionless).
6. RMS Phase Index (σφ) : Phase scintillation index, defined as the phase standard-deviation calculated from a detrended phase record of zero mean (rad). This parameter will be zero if the phase stability time entered was zero.
7. T : The strength of the (detrended) phase power-density spectrum at a fluctuation frequency of one Hertz (rad2/Hz). This parameter will be zero if the phase stability time entered was zero.
8. 10*log(T) : The T parameter in units of dB.
9. p : The (negative) slope of the single-regime phase power-density spectrum (dimensionless).
10. χ : The standard deviation of log(intensity).
11. Fade : The 95th percentile fade depth assuming that the intensity scintillation follows a Nakagami distribution within each sample record (dB).
12. Percentile : The probability that the scintillation level calculated will be exceeded expressed as the percent of time it is expected to be exceeded (percent).