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Remote Sensing of the Ocean and Atmosphere:. John L. Wilkin. [email protected] IMCS Building Room 214C 609-630-0559 (g-voice). Orbits and Measurement Geometry (1).

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Remote Sensing of the Oceanand Atmosphere:

John L. Wilkin

[email protected] Building Room 214C609-630-0559 (g-voice)

Orbits and Measurement Geometry (1)


The flow of information from land or sea surface to satellite to user depends on features of the land/ocean phenomena, the observing system, and the intervening atmosphere.

(3) Sensor: the data is a measurement or image

(4) resolution: FOV, aperture, scan geometry can depend on satellite trajectory and altitude (orbit), pointing

(2) Water leaving signal: WLR can depend on relative position of sun and satellite, time of day, emissivity, reflectance

(5) Geolocation: position, time, pointing. Orbit affects repeat sample interval

(6) Position of the satellite, or range to target may be the actual data.

(1) Ocean phenomena: color, temperature, roughness, height


Johannes Kepler (1571 – 1630) German mathematician, astronomer and astrologer

  • Planets move in elliptical orbits with the sun as one focus
  • the radius vector from the sun to the planet sweeps out equals areas in equal times
  • T2 : R3 ratio is constant for all planets, where T is orbital period and R is semi-major axis of the orbit

Isaac Newton (1643 - 1727) English physicist, mathematician, astronomer, theologian)

  • Newton discovered the laws of gravitation and explained planetary and satellite orbits in terms of the balance of forces:
  • Centripetal acceleration
  • Gravity

Galileo Galilei (1564 - 1642)Italian physicist, mathematician, astronomer, and philosopher

Galileo\'s pupil Vincenzo Viviani stated that Galileo had dropped balls of the same material, but different masses, from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass.

This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight.

There is no account by Galileo himself of such an experiment, and it is generally accepted that it was at most a thought experiment which did not actually take place.




change in velocity (acceleration) is perpendicular to the direction of travel





Δs = rΔθ



Remote Sensing of the Ocean and Atmosphere:

John L. Wilkin

[email protected] Building Room 214C609-630-0559 (g-voice)

Orbits and Measurement Geometry (2)



Stewart, R. H., 1985, Methods of Satellite Oceanography, University of California Press, 360 pp.


Right ascension - declination coordinate system

First Point of Aries: One of the two points on the Celestial Sphere where the Ecliptic and the Celestial Equator cross one another.

Ecliptic: An imaginary line in the sky that approximates the plane in which the planets orbit the Sun. From the perspective of an observer on Earth, the planets and the Sun will always remain close to this line.

When the Sun reaches the First Point of Aries, as it does once each year, the Northern hemisphere Vernal Equinox occurs.

The First Point of Aries, which is actually in Pisces, defines the zero-point for Right Ascension.

Right ascension: the celestial equivalent of longitude (starting at the First Point of Aries)

Declination: the celestial equivalent of latitude

The celestial north pole is at declination +90


    • See graphics of orbital elements and data for ISS

OSTM / Jason-2 Boost Profile

Space craft separation:


Jason-1 launch from Vandenburg Air Force Base, California

Launch: **

Other launches:

Delta-II (Themis):

Ariane launch failure:

Jason-2 OSTM

Pegasus vehicle aircraft launch

Space craft separation:


On Jan 11, 2007, China tested anantisatellite rocket. The initial collisionadded 800 to 1000 pieces of space junkto the current total of “detectable” objects.

How many detectable objects (> 4inches) are in orbit?

Collisions between existing debrisgenerate additional pieces of debris.There is concern that eventually a chainreaction will ensue (the Kesslersyndrome) littering the low earth orbit(LEO) with debris making it almostimpenetrable to new satellite launches forfear of collision.

Kessler, D. J., and Burton G. Cour-Palais. "Collision frequency of artificial satellites – The creation of a debris

belt." Journal of Geophysical Research Vol. 83 (June 1978): 2637-2646.


SeaWiFS daily coverage

seawifs_daily_coverage animation

Is this orbit prograde or retrograde?


Terra satellite, MODIS instrument, coverage of all instrument swaths during a single day ( 01/28/2006 )


ENVISAT 35-day repeat

Jason altimeter satellite

Equatorial separation of Jason groundtracks is 315 km


Sidereal day = time it takes for Earth to rotate through 360o This is slightly shorter than a solar day (24 hours)

There are 365.25 solar days in a year but 366.25 sidereal days

Sidereal day = 365.25/366.25*24 = 23.93 hours




Hohmann Transfer

Maneuver to different inclination


Scan geometry

  • zenith angle w.r.t. satellite nadir
  • look angle and solar zenith angle w.r.t local vertical
  • Fixed solid angle Field of View (FOV) such as for an optical lens, gives elliptical footprint off-nadir and varying spatial resolution in the scan

Panoramic distortion


Pixels 2.89 times bigger

if earth flat


Panoramic distortion


Pixels 2.89 times bigger

if earth flat

Pixels 4.94 times bigger

if earth round






View satellite orbits and ground tracks at:

internet resources on orbits and satellites
Internet resources on orbits and satellites
  • ground tracks and 3-D orbits for all satellites
    • Notice the clusters of satellites in the major categories or orbits
      • Geostationary
      • Polar orbiting (NOAA, Topex, ERS, Envisat)
      • Low Earth orbit (Iridium, HST, ISS)
      • GPS
    • Unusual orbits (especially ground track)
      • Chandra
      • IMAGE
      • CRRES (in a geosynchronous transfer orbit)
  • http://heavens-above.comShows predicted orbits and visibility magnitudes and star charts of pass trajectories for all satellites
    • See Homework 1
    • See graphics of orbital elements and data for ISS
  • Real-time satellite tracking at