Starting with the NOAA-K spacecraft, scheduled for launch after 1993, the AVHRRs will be replaced by a six-channel instrument, AVHRR/3 (e.g., Sparkman 1989).
The main change consists of the introduction of a new channel at 1.6 
m, the data from which will replace those from the
3.7-m channel during the sunlit portions
of each orbit. The saturation temperature of the infrared channels will be increased to ~335K, and the dark-response of the shortwave channels will be improved
to give better aerosol detection.
At the end of 1997, the morning (07:30) NOAA satellite is scheduled to be replaced with the European POEM-1 (Polar Orbit Earth Observation Mission), which
will include further AVHRR development (AVHRR-4) with seven full-time channels in the visible and infrared (e.g., NASA 1991). The spatial resolution will remain
1 
, and the data will be digitized to 12-bits.
The first EOS-A observatory is scheduled for launch toward the end of 1998 and will carry the first MODIS-N (Moderate Resolution Imaging Spectrometer-Nadir).
This is an imaging radiometer with 36-channels in the visible and infrared (0.4 to 14.54 m). The spatial resolution will be
250 in the visible and 1 km
in the thermal infrared, with a swath width of ~2300 km. The same platform will also carry the MODIS-T (MODIS-Tilt). MODIS-T concentrates 32 channels in the
visible part of the spectrum (0.4 to 0.88 m), with a spatial resolution of 1.1 km and a swath width of ~1500 km. The scan mirror mechanism also provides for
a fore-aft tilt of +67.5, -50
to avoid sun-glint over the oceans, to examine bidirectional reflectance, and to use the moon as a reference calibration target.
Further details of these two instruments are given in the EOS reference Handbook (NASA 1991).
