The 10-channel EPIC spectroradiometer is shown in Figure 9 and described in some detail in Appendix A. It spans the wavelength range from the ultraviolet to the near infrared (317.5, 325, 340, 388, 393.5, 443, 551, 645, 870, and 905 nm, see Table A-1). To view the Earth, EPIC contains a state of the art 2048 x 2048 CCD detector that has been modified to be very sensitive over the entire wavelength range. Because of the 12-inch telescope optics, the 4 million CCD elements map the Earth with a resolution of about 8 km. The real resolution is somewhat less, about 10 km at the center of the Earth and larger near the edges. The decrease in resolution from 8 to 10 km arises primarily from the "point-spread function" of the optics. A summary comparison of EPIC with some other satellite instruments is given in Table 1.
| Triana at L-1 | TOMS at LEO | GOES at GEO | |
| Spatial Coverage | Whole sunlit Earth Every hour |
80% of sunlit Earth Once per day (11:30) |
1/3 of Earth every 15 min, No Polar View |
| Spatial Resolution | 8-14 km | 45 to 90 km | 1 km visible; 4 to 8 km IR |
| Type of Measurement | UV to Near-IR Filter Instrument, 10 Channels, 317 to 905 nm |
UV Grating Spectrometer, 6 Channels, 308 to 360 nm |
1-Visible; 4- IR |
| Frequency of Measurement | RGB every 15 minutes, 10 Channels every hour for each of 4,000,000 scenes |
6 channels once per day for each of 52,000 Earth scenes | 5 channels every 15 minutes;Visible channel > 50,000,000 scenes |
| Science quantities | Ozone, Sulfur Dioxide (SO2), Aerosols (dust, smoke, and pollution), Cloud Height, UV Radiation at the Ground, Cloud Transmittance and Reflectivity, Cloud Distribution, Cloud Optical Depth, Volcanic ash (hourly aircraft hazard warning) Precipitable Water With auxiliary data: Cloud Phase Cloud Particle Shape, Surface Retro-reflection |
Ozone, Sulfur Dioxide (SO2), Aerosols (dust, smoke, and pollution), UV Radiation at the Ground, Cloud Transmittance and Reflectivity Volcanic Ash once per day |
Cloud Distribution, Cloud Height, Cloud Particle Size, Cloud Optical Depth, Aerosols over Ocean, Surface Reflectance, Surface Temperature Fire Detection, Storm Tracking |
| Main Advantage | Whole-Earth coverage from Sunrise to Sunset; First mission to measure hourly changes in ozone, clouds & aerosols over the whole globe Fixed azimuth angle |
Highly stable and accurate instrument suitable for trend studies; enables estimates of surface UV radiation Nearly constant solar zenith angle |
High spatial and temporal resolution; views day and night Fixed viewing zenith angle |
| Main Disadvantages | Unproven stability; not known if level of accuracy will be sufficient for ozone trend studies | Low spatial resolution and only 1 measurement per day at each geographic location | Views only 1/3 of Earth with no views of polar regions; 5 platforms are needed to cover globe allowing for overlap; Visible channel accuracy of 3% |
