Moderate-resolution imaging spectroradiometer
MODIS ( Moderate-resolution Imaging Spectroradiometer ) is a scientific instrument for measuring electromagnetic radiation. The translation of the term refers to a medium resolution imaging radio spectrometer. MODIS was launched into orbit by NASA on the Terra (1999) and Aqua (2002) satellites .
The instruments are designed to record large-scale geodynamic processes, including changes in cloud cover and the radiation budget, but also to provide information about the deeper atmosphere or oceans . The MODIS instrument provides high radiometric sensitivity (12 bit) in 36 spectral bands in the range from 0.4 to 14.4 µm. The response behavior has been specially adapted to the needs of the user and responds very little to signals from other frequency bands. Acquisition takes place in two bands with a nominal resolution of 250 m nadir , in 5 frequency bands the recording takes place with 500 m resolution and the remaining 29 bands work with a resolution of one kilometer. Using a ± 55-degree recording pattern at the EOS orbit altitude of 705 km, a 2330 km wide strip is recorded, with which the earth's surface can be completely recorded every two days.
construction
A rotating, double-sided mirror is used in the assembly of the receiving mirror in order to be able to cover a range of ± 55 °. It is driven by a motor that will work continuously for the entire estimated service life of the device (6 years). The optical system consists of an afocal, two-mirror off-axis telescope, which directs the energy to four refractive lens assemblies. These are VIS, NIR, SWIR / MWIR and LWIR, which cover the spectral ranges from 0.4 to 14.4 µm.
A passive high-performance cooler ensures a working temperature of 83K for the 20 infrared spectral bands on two HgCdTe focus plane assemblies (FPA for focal plane assembly). A new type of silicon-based photocell readout technology for visible light and for near infrared light leads to a previously unattained quantum efficiency with low noise and an extraordinary dynamic range. Gain and zero point can be programmed analogously. Amplifier electronics and timing are located in dedicated electronics modules in the immediate vicinity of the FPAs, the space-viewing analog module (FAM) and the forward-viewing analog module (FAM). The third module, the main electronics module, controls the energy supply, monitors the system, carries out commands and telemetry activities and contains the calibration electronics.
The system also has four on-board calibrators and also takes a look into space: They are: a solar diffuser (SD), a V-groove blackbody, a spectroradiometer calibration module (SRCA) and a monitoring unit the solar radiation stability (Solar Diffuser Stability Monitor SDSM).
The first MODIS flight instrument (PFM for Protoflight Model) is on board the Terra EOS AM-1 satellite. Terra was successfully put into operation on December 18, 1999. The second MODIS flight instrument, Flugmodell-1 or FM1, is part of the Aqua EOS PM-1 satellite; it was successfully put into operation on May 4, 2002.
Technical specifications
| Specifications | |
|---|---|
| Orbit | Altitude: 705 km, 10:30 declining knot (Terra) or 13:30 ascending knot (Aqua), sun-synchronized, polar close, circular |
| sampling rate | 20.3 / min, across the web |
| Strip width | 2330 km (across the track) by 10 km (viewed from the vertical along the track) |
| Dimensions | |
| telescope | 17.78 cm in diameter; off-axis, afocal (collimated), with medium field limitation |
| Dimensions | 1.0 × 1.6 × 1.0 m |
| Weight | 228.7 kg |
| power | 162.5 W (average over a radius) |
| Data rate | 10.6 Mbit / s (peak value during the day); 6.1 Mbit / s (mean) |
Web links
- Official NASA website NASA
- MODIS frequency bands and spectral range USGS
- The MODIS picture of the day NASA
- MODIS Rapid Response system (makes images available almost in real time) rapidfire
- Image data from MODIS that can be zoomed using a Flash application. flashearth
- Web service for MODIS image data NASA
- The latest MODIS images NASA