Emilyyu/doppler shift calc changes

gs/backend/positioning/doppler_shift.py

@@ -0,0 +1,107 @@
+from typing import Final
+
+from skyfield.api import EarthSatellite, Time, Timescale, Topos
+
+SPEED_OF_LIGHT_METERS_PER_SECOND: Final[int] = 299_792_458
+TRANSMISSION_FREQUENCY_HZ: Final[float] = 433_920_000  # Default frequency, UW-Orbital's 433.920 MHz band
+
+"""
+@brief Holds logic for calculating doppler shift from TLS and ground station coordinates
+@details Since we're not actually getting TLE or interfacing with HackRF it's not hooked up to anything yet
+"""
+
+
+# Change: made function take in time as a parameter instead
+def load_satellite(tle_line1: str, tle_line2: str, timescale: Timescale, name: str = "UW_SAT") -> EarthSatellite:
+    """
+    @brief Loads satellite from TLE lines
+    @param tle_line1: First line of TLE
+    @param tle_line2: Second line of TLE
+    @param timescale: Time for which satellite position is being calculated
+    @param name: Optional satellite name
+    @returns EarthSatellite object
+    """
+    return EarthSatellite(tle_line1, tle_line2, name, timescale)
+
+
+# Change: made function take in time as a parameter
+def calculate_relative_velocity(
+    satellite: EarthSatellite,
+    observer_latitude_deg: float,
+    observer_longitude_deg: float,
+    observer_altitude_m: float,
+    time_current: Time,
+) -> float:
+    """
+    @brief Computes relative velocity between satellite and observer
+    @param satellite: EarthSatellite object
+    @param observer_latitude_deg: Latitude of observer in degrees
+    @param observer_longitude_deg: Longitude of observer in degrees
+    @param observer_altitude_m: Altitude of observer in meters
+    @param time_current: Time for which relative velocity is being calculated
+    @returns Relative radial velocity in m/s (positive is moving away)
+    """
+
+    observer = Topos(
+        latitude_degrees=observer_latitude_deg,
+        longitude_degrees=observer_longitude_deg,
+        elevation_m=observer_altitude_m,
+    )
+    difference = satellite - observer
+    topocentric = difference.at(time_current)
+
+    # Separate velocity and position vectors
+    vx, vy, vz = topocentric.velocity.km_per_s
+    vel: tuple[float, float, float] = (vx, vy, vz)
+
+    px, py, pz = topocentric.position.km
+    pos: tuple[float, float, float] = (px, py, pz)
+
+    # Normalize position
+    pos_mag = sum(p**2 for p in pos) ** 0.5
+    los_unit = [p / pos_mag for p in pos]
+
+    # Radial velocity = dot product of velocity vector with line-of-sight unit vector
+    radial_velocity_km_s = sum(vel[i] * los_unit[i] for i in range(3))
+
+    return float(radial_velocity_km_s * 1000.0)  # km/s -> m/s
+
+
+def compute_doppler_shift(frequency_hz: float, relative_velocity_m_s: float) -> float:
+    """
+    @brief Computes the Doppler-shift frequency
+    @param frequency_hz: Transmission frequency in Hz
+    @param relative_velocity_m_s: Relative radial velocity in m/s
+    @returns Doppler-shift frequency in Hz
+    """
+    return frequency_hz * (
+        SPEED_OF_LIGHT_METERS_PER_SECOND / (SPEED_OF_LIGHT_METERS_PER_SECOND + relative_velocity_m_s)
+    )
+
+
+# Change: made trans freq a constant in the file that is passed instead of a parameter to the function
+def calculate_doppler(
+    tle_line1: str,
+    tle_line2: str,
+    observer_latitude_deg: float,
+    observer_longitude_deg: float,
+    observer_altitude_m: float,
+    timescale: Timescale,
+    time_current: Time,
+) -> float:
+    """
+    @brief High-level function to compute Doppler shift
+    @param tle_line1: First line of TLE data
+    @param tle_line2: Second line of TLE data
+    @param observer_latitude_deg: Latitude of observer in degrees
+    @param observer_longitude_deg: Longitude of observer in degrees
+    @param observer_altitude_m: Altitude of observer in meters
+    @param timescale: Time for which satellite position is being calculated
+    @param time_current: Time for which Doppler shift is being calculated
+    @returns Doppler-shifted frequency in Hz
+    """
+    sat = load_satellite(tle_line1, tle_line2, timescale)
+    rv = calculate_relative_velocity(
+        sat, observer_latitude_deg, observer_longitude_deg, observer_altitude_m, time_current
+    )
+    return compute_doppler_shift(TRANSMISSION_FREQUENCY_HZ, rv)