Crossing Times

	Swath Time Labels
	Polar Orbits (SSM/I, AMSR-E, QuikScat, SeaWinds)
	Near-equatorial Orbits (TMI)

Swath Time Labels

Quikscat daily images and AMSR daily images (click for large view) have UTC time labeled under each swath. SSM/I dynamic daily and AMSR dynamic daily swaths are labeled according to the UTC time the satellite crossed the top and bottom edge of the subset image. TMI dynamic daily swaths are labeled on all four edges of the subset image. By adjusting the image size and location, dynamic imaging can be used to find the UTC minute a satellite passed over a particular area on earth.

Polar Orbits (SSM/I, AMSR-E, QuikScat, WindSat)

A polar-orbiting satellite is placed in a circular sun-synchronous orbit, typically at a low altitude of 700 to 800 km. It usually takes about 100 minutes to make one trip around the earth, allowing for just over 14 orbits daily. These satellites cross the equator at the same local solar time each day, once ascending (traveling from south to north) and once descending. A good description of this type of orbit is provided by the Naval Research Lab, Monterrey: Navy Forecaster's Guidance: General Description of Polar Orbiting Satellites

We provide data from the DMSP polar orbiters hosting the SSM/I instruments and the QuikScat platform hosting the SeaWinds scatterometer. Sun-synchronous orbits are often described by their equatorial crossing times. The equatorial crossing times remain nearly constant throughout the year. However, orbit degradation can cause a slow change in this value over time. Listed below are the ascending and descending equatorial crossing times for each currently functioning instrument on our web page. The plot shows the change over time of the ascending equatorial crossing times. Some satellite orbits are more stable than others and little change occurs over the years of operation.

Equatorial Crossing Times (Local Solar Time) as of July, 2010

Platform	Instrument	Ascending	Descending
Aqua	AMSR-E	13:36	01:36
DMSP F15	SSM/I	17:16	05:16

Near-equatorial Orbits (TMI)

The TMI instrument is in a near-equatorial orbit. This type of orbit crosses the equator at varying times throughout the day. A good discussion of the TRMM orbit overflights is provided by NASA: TRMM Local Times of Overflights Notes

Last updated: July 29, 2010