Solar occultation method
Solar occultation is a technique in which the transmission of sunlight through the Earth's atmosphere is measured and ratioed to exoatmospheric measurements (solar measurements recorded with no atmospheric attenuation). This is carried out at a series of tangent heights, increasing in altitude during a sunrise or decreasing in altitude during a sunset. From each of the atmospheric measurements a slant column is calculated which can contain contributions from multiple atmospheric layers. The slant columns contain sufficient information that when combined and inverted, one can obtain a profile of the atmosphere.
ACE sunset occultation diagram
Orbit
The 74° orbit was chosen as the optimum inclination to achieve a combination of numerous measurements, global coverage and high latitude extension. The latitude of occultation measurements possible from the SCISAT orbit (see figure) essentially repeats itself every year.
Inclination (i): 74 degrees
Altitude (h): 650 km
Orbit Eccentricity (e): 0 (circular)
Orbital Period: 97.7 minutes
Orbital Lifetime > 5 years
Occultation latitude as a function of date for the SCISAT satellite:
