added covarage

api/app/core/atmosphere.py

@@ -1,6 +1,31 @@
+from __future__ import annotations
+
+from itur.models import itu676
+
+from app.core.geo import GeoPoint, haversine
+
+
 def p676_gas_attenuation(freq_hz: float, distance_km: float) -> float:
     if freq_hz <= 0:
         raise ValueError("freq_hz must be positive")
     if distance_km < 0:
         raise ValueError("distance_km must be non-negative")
-    raise NotImplementedError("ITU-R P.676 gas attenuation requires pycraf integration")
+    if distance_km == 0:
+        return 0.0
+
+    freq_ghz = freq_hz / 1_000_000_000
+    attenuation = itu676.gaseous_attenuation_terrestrial_path(
+        distance_km,
+        freq_ghz,
+        0,
+        7.5,
+        1013,
+        288,
+        "exact",
+    )
+    return float(attenuation.value)
+
+
+def atmospheric_loss_between(tx: GeoPoint, rx: GeoPoint, freq_hz: float) -> float:
+    distance_km = haversine(tx, rx) / 1000.0
+    return p676_gas_attenuation(freq_hz, distance_km)