Ocean Color and Temperature Scanner (OCTS)

Observation Concept

Ocean Color and Temperature Scanner (OCTS) is an optical radiometer to achieve highly sensitive spectral measurement with 12 bands covering visible and thermal infrared region. In the visible and near-infrared bands, the ocean conditions are observed by taking advantage of spectral reflectance of the dissolved substances in the water and phytoplankton. On the other hand, the sea surface temperature is accurately measured in 4 thermal infrared bands.
As the swath width of OCTS is about 1,400km with scanning mirror (west-east) and OCTS also scans south and north, it can observe the entire earth surface for 3 days. The spatial resolution is about 700m.

OCTS observation concept.

The satellite flying over the equator cannot get inforamtion on the ocean because of direct sunglitter at the sea surface. In order to prevent this sunglitter from interrupting the observation, OCTS can tilt its field of view along the track by +/- 20 degrees.
It is likely that sensor performance is subject to the unique space environmental factors, such as radiation, affecting detector sensitivity and mirror transmittance. OCTS has optical calibration functions using solar light and halogen lamp so as to perform as planned in visible and near-infrared bands. For example, when the satellite passes over the north pole, solar light enters the solar calibration module so that the deep space and black body are observed every rotation of a mirror so as to calibrate differences between lower temperature and ambient temperature.
In addition, OCTS has electrical calibration functions to confirm performance of the electrical unit. OCTS has two data transmission modes. All raw pixel data is transmitted via Direct Transmission Subsystem (DT) or Inter Orbit Communication Subsystem (IOCS) in fine data transmission mode. One pixel data is sampled from every 6 x 6km area as typical data of the area and is downlinked to the local users (ex. fishery ships) via Direct Transmission to Local Users (DTL) in coarse data transmission mode.

Planned Missions

OCTS mainly serves as an observation sensor of the ocean conditions, including chlorophyll and dissolved substances in the water, temperature profile and cloud formation processes. The ocean has great effects on our lives as well as the natural environment. Ocean surface temperature substantially interrelates with the global temperature changes since approximately 70% of the earth is coverd with the oceans. It is also important to get information on ocean primary production. OCTS data will prove to be of great use for understandings of the ocean conditions and phenomena.

Note) Phytoplankton in the ocean convert nutrients into plant material which feeds various fishes, such as sardines and tuna. Thus, Phytoplankton is an indicator of ocean productivity.

Configuration and Performance

OCTS consists of a Scanning Radiometer Unit (SRU), which contains optical system, and an Electrical Unit (ELU) for digital signal processing and other functions.

Internal configuration of SRU.

The scanning mirror reflects observation light to focus on Optics Assembly. The mirror is electrically rotated per second and scans a line at forward and backward tilt within +/- 20 degrees. In the Optics Assembly, light is converged through Ritchie-Chretien telescope and then splitted to two visible-near infrared bands and a infrared band through a dichroic filter. In Visible and Near Infrared Detector Assembly, optical signals are converted electrically.
The infrared detector is cooled at 100K by a large radiation cooler. It faces the deep space at temperature of 4K, and emits heat of the detector. The electrical signals are amplified by the specefied gain in Analog Signal Processor, and then converted to digital signals. The digital signals processed in Digital Signal Processor are transmitted to bus module.

Earth Observation Research Center
Comments to: adeossupport@eorc.nasda.go.jp
Last Update: 5 Febrary 1998