Mission concept and assessment

Example 1 The flight window for 15 October 2026 in Bangkok

The team starts 15 minutes after sunrise and stops 15 minutes before sunset so that there is enough light for images, and intersects this with the legal hours.

import math
from datetime import date

LAT, LON, TZ = 13.75, 100.50, 7
DAY = date(2026, 10, 15)
BUFFER = 15                                    # minutes

def sunrise_sunset(lat, lon, day, tz):
    g = 2 * math.pi / 365 * (day.timetuple().tm_yday - 1)
    eqt = 229.18 * (0.000075 + 0.001868 * math.cos(g) - 0.032077 * math.sin(g)
                    - 0.014615 * math.cos(2 * g) - 0.040849 * math.sin(2 * g))
    decl = (0.006918 - 0.399912 * math.cos(g) + 0.070257 * math.sin(g) - 0.006758 * math.cos(2 * g)
            + 0.000907 * math.sin(2 * g) - 0.002697 * math.cos(3 * g) + 0.00148 * math.sin(3 * g))
    phi = math.radians(lat)
    h = math.degrees(math.acos(math.cos(math.radians(90.833)) / (math.cos(phi) * math.cos(decl))
                               - math.tan(phi) * math.tan(decl)))
    rise = 720 - 4 * (lon + h) - eqt + tz * 60
    sset = 720 - 4 * (lon - h) - eqt + tz * 60
    return rise, sset

def hhmm(m):
    return f"{int(m // 60):02d}:{int(round(m % 60)):02d}"

rise, sset = sunrise_sunset(LAT, LON, DAY, TZ)
start = max(6 * 60, rise + BUFFER)
end = min(18 * 60, sset - BUFFER)
print(f"sunrise {hhmm(rise)}, sunset {hhmm(sset)}")
print(f"flight window {hhmm(start)}-{hhmm(end)} ({(end - start) / 60:.1f} h)")

sorties = [(3189, 3), (3144, 2), (3055, 3), (2130, 2)]   # m, inspection points (from UAT 304 Module 3)
SPEED, HOVER_MIN, SWAP_MIN = 8, 1.0, 15
t = 8 * 60                                     # start at 08:00
for k, (length, n) in enumerate(sorties, 1):
    fly = length / SPEED / 60 + n * HOVER_MIN
    print(f"sortie {k}: {hhmm(t)}-{hhmm(t + fly)} ({fly:.1f} min)")
    t += fly + SWAP_MIN
print(f"finished by {hhmm(t - SWAP_MIN)}, inside window: {t - SWAP_MIN <= end}")

sunrise 06:08, sunset 17:59
flight window 06:23-17:44 (11.3 h)
sortie 1: 08:00-08:10 (9.6 min)
sortie 2: 08:25-08:33 (8.6 min)
sortie 3: 08:48-08:58 (9.4 min)
sortie 4: 09:13-09:19 (6.4 min)
finished by 09:19, inside window: True

All four sorties finish well before noon, but a free window all day does not mean flying is possible all day. In the rainy season, thunderstorms often build in the afternoon, so the team schedules work in the morning and keeps spare time in case it must postpone.

Example 2 Proceed or postpone?

Team limits: mean wind up to 10 m/s, gusts up to 12 m/s, visibility at least 5 km, and no thunderstorm (hypothetical data).

KT, KMH = 0.5144, 1 / 3.6
LIMITS = {"wind": 10.0, "gust": 12.0, "vis_km": 5.0}
sources = {   # source: values converted from original units to m/s and km
    "airport METAR 08:00": {"wind": 12 * KT, "gust": 22 * KT, "vis_km": 10, "ts": False},
    "site anemometer 08:10": {"wind": 6.5, "gust": 11.8, "vis_km": None, "ts": False},
    "forecast 14:00": {"wind": 20 * KMH, "gust": 50 * KMH, "vis_km": 6, "ts": True},
}

def decide(names):
    worst_wind = max(sources[n]["wind"] for n in names)
    worst_gust = max(sources[n]["gust"] for n in names)
    vis = [sources[n]["vis_km"] for n in names if sources[n]["vis_km"] is not None]
    reasons = []
    if worst_wind > LIMITS["wind"]:
        reasons.append(f"wind {worst_wind:.1f} m/s")
    if worst_gust > LIMITS["gust"]:
        reasons.append(f"gust {worst_gust:.1f} m/s")
    if vis and min(vis) < LIMITS["vis_km"]:
        reasons.append(f"visibility {min(vis)} km")
    if any(sources[n]["ts"] for n in names):
        reasons.append("thunderstorm")
    return ("GO" if not reasons else "NO-GO"), reasons, worst_wind, worst_gust

for label, names in (("morning", ["airport METAR 08:00", "site anemometer 08:10"]), ("afternoon", ["forecast 14:00"])):
    d, why, w, g = decide(names)
    print(f"{label:<9} worst wind {w:.1f} m/s, gust {g:.1f} m/s -> {d} {why if why else ''}")

morning   worst wind 6.5 m/s, gust 11.8 m/s -> GO
afternoon worst wind 5.6 m/s, gust 13.9 m/s -> NO-GO ['gust 13.9 m/s', 'thunderstorm']

The morning passes, even though the gust at the site is close to the limit. The afternoon fails on both the gust and the thunderstorm. Recording reasons like this means that if anyone later asks why the team did or did not fly, it can answer with data rather than feelings.