← INDEX — FIG. 00 — 705 KM · 98.2° · 10:12 AM
J₂ = 1.0826 × 10⁻³
SUNSYNC
EARTH OBSERVATION SATELLITES
Landsat 9 crosses the equator at 10:12 every day.
BEGIN — CHAPTER 01 →CH.01 / 06 — SAME LIGHT EVERY DAY
Comparing pictures needs the same shadows
Sun-synchronous orbits keep the same light.
Landsat 1 (1972) and Landsat 9 (2021).
CH.02 / 06 — A DEGREE A DAY
Let Earth's bulge turn the orbit
The Sun's direction drifts 0.986° a day.
Choose the inclination for 0.986°/day.
NODAL PRECESSION FROM J₂ (CIRCULAR ORBIT)
dΩ/dt = −(3/2) n J₂ (R/a)² cos i · sun-synchronous: dΩ/dt = 360°/365.2422 d
Standard geodetic constants.
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CH.03 / 06 — STRIPES AROUND THE WORLD
Swath width sets the revisit time
Landsat 16 days, Sentinel-2 10 days (5 with two).
Swath vs resolution vs altitude.
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Rough revisit estimate.
CH.04 / 06 — HOW SHARP CAN IT BE
Diffraction sets a floor
Landsat 30 m, Sentinel-2 10 m.
Thermal infrared is coarser.
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CH.05 / 06 — HALF A CENTURY OF THE SAME VIEW
The longest record of Earth from space
The same light, every day for fifty years.
CH.06 / 06 — REFERENCES