The short answer is that, under the hood, dopplershift will compute the instantaneous frequency shift any time there is geometric line‐of‐sight (i.e. elevation > 0°), but it does not automatically apply your MinElevationAngle setting on the groundStation object. That property is used by coverage‑ and access‑type analyses (e.g. coverage, access) and your scenario viewer, but not by the raw doppler‑shift calculator.
You have two straightforward ways to mask out any samples below your 30° (minelevation) elevation threshold:
- You can use lookAngles to get elevation and then mask. Here is a pesudo MATLAB code for the same:
% 1) Here, we compute doppler
[frequencyShift, timeOut, dopplerInfo] = dopplershift(sat, gs, Frequency=carrierFrequency);
% 2) Then we compute elevation angles at the same time points
[~, elevationDeg, ~] = lookAngles(gs, sat);
% 3) Zero‐out (or NaN‐out) everything below your minelevation
maskLow = elevationDeg < minelevation;
frequencyShift(maskLow) = NaN;
2. You can also use access intervals to find "valid" windows. If you want to work with time intervals rather than per-sample elevations, you can use access function which does respect your MinElevationAngle.
Here's the MATLAB code for the same:
% Getting the access intervals (as datetime pairs)
[acStart, acEnd] = access(sat, gs);
% Pre‑allocation of your masked doppler array
[frequencyShift, timeOut, ~] = dopplershift(sat, gs, Frequency=carrierFrequency);
frequencyShiftMasked = NaN(size(frequencyShift));
% For each access window, copy across the valid doppler samples
for k = 1:numel(acStart)
idx = (timeOut >= acStart(k)) & (timeOut <= acEnd(k));
frequencyShiftMasked(idx) = frequencyShift(idx);
end
% frequencyShiftMasked now has NaNs outside elevation ≥30°
The dopplershift function is intended to give you the pure physics‑only Doppler profile under any direct line‐of‐sight. In MATLAB’s design, things like minimum elevation angles, atmospheric masks, antenna patterns, etc., are orthogonal “coverage” attributes that you layer on afterwards (via access, coverage, or graphical filters).
Hope it helps!
