ADEOS (Advanced Earth Observing Satellite) / Midori

ADEOS (Midori) is the first Japanese (NASDA) satellite mission with international cooperation. The overall objective of the mission is dedicated to Earth environmental research: integrated observation of geophysical parameters, global observation of land, ocean and atmospheric processes (ocean color and sea surface temperature). In addition, communication demonstrations are planned for the study (feasibility) of interorbit links, called IOCS (Inter-Orbital Communication Subsystem). ^{1) 2) 3)}

Note: NASDA changed its name on Oct. 1, 2003 to JAXA (Japan Aerospace Exploration Agency), Tokyo, Japan. JAXA is the new name (merger) of the three former Japanese space organizations into a single national agency, namely: NASDA (National Space Development Agency of Japan), ISAS (Institute of Space and Astronautical Science), and NAL (National Aerospace Laboratory of Japan).

Figure 1: Line drawing of the ADEOS spacecraft (image credit: NASDA)

The spacecraft is comprised of a bus with a deployable solar array (one wing). Satellite mass = 3560 kg at lift-off, payload mass = 1300 kg, power = 4.5 kW, S/C size: 4 m x 4.5 m. The spacecraft is made up of thermally, electrically and mechanically independent units, which facilitate its integration and testing, including the C&DH (Communications and Data Handling Subsystem), the EPS (Electrical Power Subsystem), and the AOCS (Attitude and Orbital Control Subsystem). ^{4) 5) 6) 7)}

The AOCS employs a three-axis strap-down attitude detection system and a zero-momentum attitude control system, attitude error t0.3º, attitude stability t0.003º/s. Mission design life=3 years.

The satellite features an automatic, autonomous operation function capable of operating a large number of mission instruments, and inter orbital communication equipment to transmit observation data via data relay satellite. The IOCS (Inter-Orbital Communication Subsystem) transmits observation data via ETS-VI (Engineering Test Satellite-VI) and COMETS (Communications and Broadcast Engineering Test Satellite).

The ADEOS spacecraft was developed by the Mitsubishi Electric Corporation, Tokyo. NEC Corporation and Toshiba Corporation were subcontractors to Mitsubishi Electric Corporation.

Orbit: Sun-synchronous sub-recurrent polar orbit; apogee = 804.6 km; perigee = 789.0 km; orbital period = 100.8 min, 10:30 AM local sun orbit (on descending node). Ground repeat cycle=41 days (subcycle = 3 days), inclination = 98.625º.

Launch: The launch of ADEOS took place on August 17, 1996 with the H-II launch vehicle from TNSC (Tanegashima Space Center), Japan.

RF communications: ADEOS provides onboard recording (MDR=Mission Data Recorder (three instruments) and LMDR = Low Speed Mission Data Recorder). Observation data rates: AVNIR (M): 60 Mbit/s, AVNIR (P): 60 Mbit/s, OCTS: 3.0 Mbit/s. Polder: 0.882 Mbit/s. IMG: 0.9 Mbit/s. ILAS: 0.517 Mbit/s. NSCAT: 2.9 kbit/s. TOMS: 0.7 kbit/s.

RF comuunications: TT&C: Uplink frequency (S-band) = 2.0 GHz (CMD and ranging), downlink frequency = 2.2 GHz (TLM and ranging), command bit rate = 500 bit/s.
Science data transmission: 3 X-band links (8.15, 8.25, 8.35 GHz) with QPSK modulation.

IOCS frequencies: S-band (low rate mission data), Ka-band (120 Mbit/s max).

Figure 2: Artist's rendition of the ADEOS spacecraft (image credit: JAXA)

Mission status: The ADEOS S/C operations are terminated: ADEOS operated nominally for some period (10 months), but then suffered several malfunctions and stopped functioning June 30, 1997 after an apparent loss of power due to structural damage in its solar array. This loss of an observatory like ADEOS was definitely a great blow, particularly for all involved in the mission and of course the data user community.

Sensor complement: (OCTS, AVNIR, NSCAT, TOMS, POLDER, IMG, ILAS, RIS)

OCTS (Ocean Color and Temperature Scanner), a mechanical scanning (whiskbroom) radiometer, and a NASDA core sensor. Objectives: Ocean color and sea surface temperature measurements (ocean primary productivity, interaction between the ocean and the atmosphere and environmental studies). OCTS offers 12 measurement bands from 0.402 - 12.5 µm. Swath width = 1400 km; ±20º along-track tilting. Spatial resolution: approx. 700 m. Operation requirements: global observation of the Earth during daytime (TIR channel during night if required). ⁸⁾

Table 1: Definition of OCTS parameters

The OCTS sensor consists of a scanning radiometer with an optical system, a detector module and an electrical unit. OCTS employs a catoptric optical system and a mechanical rotating scanning method with a mirror (due to wide spectral coverage). OCTS can be tilted about the along-track axis to prevent sea surface sun glitter. The IR detectors are cooled to 100 K by a large radiant cooler facing deep space. Calibration: solar and internal lamp for VNIR, deep space and black body for IR.

Figure 3: The observation concept of the OCTS instrument

Figure 4: Internal configuration of the SRU (SCanning Radiometer Unit) of OCTS (image credit: NASDA)

AVNIR (Advanced Visible and Near-Infrared Radiometer) a NASDA core sensor, an optoelectronic scanning radiometer using CCD detectors. Objective: Land and coastal zone observations, measurement of reflected sunlight from the Earth's surface. AVNIR is comprised of two units, SRU (Scanning Radiometer Unit) containing all the optical components (a catadioptric Schmidt telescope system is used, the spectrum is dispersed by a prism and interference filter), and ELU (Electronic Unit). ⁹⁾

Spectral range: 5 bands from 0.42 - 0.89 µm (multispectral bands: 0.42-0.50, 0.52-0.60, 0.61-0.69 and 0.76-0.89 µm, panchromatic band (visible): 1 band 0.52-0.69 µm). Spatial resolution: multispectral bands: ~16 m (IFOV=20 µrad), panchromatic band: about 8 m (IFOV =10 µrad). Swath width = 80 km (FOV=5.7º). Observation requirements: regional observation according to user requests; simultaneous multispectral and panchromatic operation.

The AVNIR instrument has the capability to tilt the observation field by ±40º about the across-track axis. The 0.42-0.50 µm band is useful for coastal zones and lakes. The scanning radiometer unit uses a catadioptric Schmidt optical system (telescope) to reduce aberration in a wide field of view. Calibration of sensor using solar light and internal lamps. The radiometric absolute accuracy is ±10%, the onboard calibration accuracy =±5%. The large linear array CCDs offer 5,000 and 10,000 detector elements for high spatial resolution. Instrument mass=250 kg, power=300W.

Figure 5: The observation geometries of the AVNIR instrument

Figure 6: Illustration of the AVNIR instrument (image credit: NASDA)

Figure 7: Block diagram of the AVNIR instrument (image credit: NASDA)

NSCAT (NASA Scatterometer) a NASA/JPL sensor. Objective: Measurement of surface wind speeds and directions over the global oceans, coverage every two days under all weather and cloud conditions. NSCAT is a microwave radar instrument (a fan-beam Doppler scatterometer), using an array of six antennas that radiate microwave pulses at a frequency of 13.995 GHz across broad regions of the Earth's surface. An array of six, 3 m long antennas scan two swaths of 600 km width each, one band to each side of the flight path, separated by a gap of 330 km at nadir. Wind speed accuracy = 2 m/s (rms), direction accuracy = 20º (rms), resolution = 50 km; antenna polarization: 6 V, 2 H; antenna beam width=25º (3 dB broad beam) =0.42º (3 dB narrow beam); instrument mass=300 kg; power=275 W; data rate = 2.9 kbit/s; peak transmit power=110 W; pulse width=5 ms; PRF=62 Hz. Operation requirements: continuous operation for global observation of the oceans (about 190,000 wind measurements/day). Note: NSCAT is an upgraded version of the Radar Scatterometer (SASS) on SEASAT. ^{10) 11)}

Figure 8: Illustration of the NSCAT antenna radiation pattern geometries (image credit: NASA)

NSCAT transmits microwave pulses and receives a backscattered echo from the ocean surface. Changes in wind velocity cause changes in ocean surface roughness, modifying the radar cross section of the ocean and the magnitude of the backscattered power. Multiple collocated measurements acquired from several directions can thus be used to solve for wind speed and direction simultaneously.

Table 2: NSCAT instrument performance parameters

Figure 9: Schematic of NSCAT instrument (image credit: NASA)

TOMS (Total Ozone Mapping Spectrometer), a NASA/GSFC sensor. Objective: Observation of total ozone changes, evaluation of changes in UV radiation and the observation of sulfur dioxide. Measurement wavelengths: 308.6, 312.5, 317.5, 322.3, 331.2 and 360 nm with 1 nm bandpass. Swath width: 2795 km. IFOV= 50 km at nadir; cross-track scan = 111º (37 3º steps). Operation requirements: global observation of illuminated part. TOMS mass=34 kg, power=24 W, data rate=700 bit/s.

TOMS measures the albedo of the Earth's atmosphere at six narrow spectral bands in the near-ultraviolet region. The albedo is measured by comparing the radiance of the Earth with the radiance of a calibrated on-band diffuser plate. Total ozone is derived from the differential albedo in three pairs of spectral bands, which are selected to function at all latitudes and solar illumination conditions.

Figure 10: Illustration of the TOMS instrument (image credit: NASA)

POLDER (Polarization and Directionality of the Earth's Reflectances), a passive optical imaging radiometer of CNES (as passenger instrument on ADEOS). Objectives: Observation of bidirectionality and polarization of the solar radiation reflected by the atmosphere: tropospheric aerosols (inversion of the physical properties); ocean color (accurate determination of sea surface reflectances); land surfaces (determination of surface BRDF and improvement in the correction of the surface bidirectional and atmospheric effects on vegetation indices); Earth radiation budget (determination of cloud BRDF and classification of clouds according to their bidirectional properties). POLDER is capable to observe an area from various directions along with the spectral characteristics of the reflected solar light. ^{12) 13)}

a) Measurement of polarized reflectance in VIS/NIR
b) Observation of the Earth's target reflectance from 12 directions during a single S/C pass
c) Operation in two dynamic modes for high SNR and wide dynamic range

Six of POLDER's eight frequencies are optimized for observing atmospheric aerosols, clouds, ocean color, and land surfaces. The other two frequencies are centered on the H₂O and O₂ absorption bands for retrieving atmospheric water vapor amount and cloud top height, respectively.

Measurement channels: 15 channels (three channels for each polarized band) Swath width = 1440 km x 2200 (across-track) km, ground spatial resolution of 7 km x 6 km at nadir. Data rate: 0.882 Mbit/s, 12 bit quantization. Operation requirements: global observation of the Earth with more than 15º of solar elevation, simultaneous operation with OCTS.

Figure 11: Observation concept of POLDER (image credit: CNES)

POLDER is a 2-D detector array wide-field-of-view, multi-band imaging radiometer/polarimeter. Multi-angle viewing is achieved by the along-track migration of the S/C of a quasi-square footprint. The optical detection unit of the POLDER consists of a telecentric lens, a rotating wheel supporting filters and polarizers, and a matrix CCD sensor (242 x 548 photoelements, the pixels are binned one by two, resulting in 242 x 274 sensitive areas). The instrument has a focal length of 3.57 mm, f/4.6, FOV=±43º along-track, FOV=±51º across-track, FOV=±57º diagonal. Instrument mass= 33 kg, power=42 W.

Table 3: Spectral characteristics of POLDER

IMG (Interferometric Monitor for Greenhouse Gases). IMG is a MITI-funded sensor developed by JAROS, this is a nadir-looking Fourier transform infrared spectrometer (FTIR)]; Objectives: Observation of detailed spectra of IR radiation of the Earth's surface and the atmosphere, mapping greenhouse gases on a global scale (CO₂, CH₄, N₂O). Continuous measurements of the infrared spectrum in the range from 3.3 - 14.0 µm with a very fine spectral resolution of 0.1 cm^-1 (apodized) absolute accuracy of measurement=t1 K, stability of measurementt0.1K, IFOV=10 mrad (~64 km² footprint); vertical resolution about 2-6 km depending on species; interferogram scan time ≤ 10 s. Operation requirements: full time operation for 3 days out of 13 days. A mechanical cryogenic coolant system is used to regulate the temperature of the quantum detectors. An image motion compensation mirror is used to compensate for the satellite orbital motion. Measurements are made in 20 km swaths at 8 km resolution.

Table 4: Some characteristics of the IMG instrument

Figure 12: The observation concept of IMG (image credit: NASDA)

IMG is a Michelson-type Fourier Transform Spectrometer (FTS) with two mirrors and a beam splitter. The incident radiation is divided by the beam splitter into two paths. One mirror is moved so that the two paths produce an interference pattern when recombined. The signal measured by the detector, the interferogram, can be Fourier-transformed to obtain the incident spectrum. The diameter of the entrance aperture is 10 cm. The moving mirror is suspended on magnetic bearings and scans a 10 cm long path in 10 seconds. ¹⁴⁾

Figure 13: Overview of the IMG FTS optical system (image credit: NASDA)

ILAS (Improved Limb Atmospheric Spectrometer), a sensor of the Environment Agency of Japan (EA), heritage of LAS on Ohzora (EXOS-C). Objectives: Measurement of atmospheric trace gases and the pressure and temperature profiles by the solar occultation technique (vertical profiles of O₃, NO₂, aerosols, H₂O, CFC11_, CH₄, N₂O). ILAS has two grating spectrometers, one is used for the IR-band trace gases, the other measures aerosols, air temperature and pressure in the VIS-band. The ILAS occultation measurements are performed only at high latitudes in both hemispheres (due to orbit characteristics). ILAS keeps looking at the sun during sunrise and sunset, it measures the sequence of spectral intensity changes in the solar light which pass through the various tangent heights of the atmosphere. Since atmospheric trace gases have their own characteristic absorption spectra, the concentration of gases can be derived from these absorption measurements. ^{15), 16), 17) 18)}

Table 5: ILAS instrument parameters

Figure 14: Illustration of the ILAS observation concept (image credit: NASDA)

Figure 15: Schematic overview of the ILAS instrument (image credit: NASDA)

RIS (Retroreflector in Space), a JEA sensor. RIS is a single element corner-cube reflector for Earth-satellite-Earth laser long-path absorption measurements of atmospheric trace gases. RIS has a hollow reflector structure with an effective diameter of 0.5 m. A spherical mirror with a very small curvature is used for one of the three mirrors forming the corner cube, in order to optimize the ground pattern of the beam reflected by RIS. Instrument mass=43 kg.

Objective: Used for laser long-path absorption measurements of atmospheric trace species and to support two color laser ranging experiments. Measurements of ozone (O₃), CFC12, HNO₃, methane (CH₄), CO, and other gases by the laser beam absorption technique. Wavelength range: 0.4 - 14 µm. - In the RIS experiments a laser beam is transmitted from a SLR ground station, reflected by RIS, and received back at the ground station. The absorption of the intervening atmosphere is measured in the round-trip optical path (measurement of absorption spectra by the Doppler shift of the reflected beam). The column contents and vertical profiles of atmospheric trace gases are obtained from the measured spectra. The RIS experiments are performed when ADEOS passes over the ground stations in Japan. The ground stations use two single-longitudinal-mode TEA-CO₂ lasers for the spectroscopic measurements. ^{19) 20) 21)}

Figure 16: Schematic configuration of the RIS corner retroreflector (image credit: NASDA)

ADEOS carries in addition TEDA (Technical Engineering Data Acquisition Equipment) to measure the space environment surrounding the S/C. TEDA monitors radiation absorption, memory malfunction, static charge voltage, and contamination, and analyzes heavy ions.

2) In Japan the ADEOS satellite is also referred to as `Midori', meaning `green'.

3) http://www.eorc.nasda.go.jp/ADEOS/Project/index.html

4) "ADEOS," NASDA brochure, 1993

5) "Special issue on ADEOS," IEEE Transactions on Geoscience and Remote Sensing, Vol. 37, No 3, May 1999, Part II of two parts

6) ADEOS Reference Handbook, 1996, online available at http://www.eorc.nasda.go.jp/ADEOS/Products/Handbook.html

7) http://www.eorc.jaxa.jp/hatoyama/satellite/satdata/adeos_e.html

8) http://www.eorc.nasda.go.jp/ADEOS/Project/Octs.html

9) http://www.eorc.nasda.go.jp/ADEOS/Project/Avnir.html

10) F. M. Naderi, M. H. Freilich, D. G. Long, "Spaceborne Radar Measurement of Wind Velocity Over the Ocean - An Overview of the NSCAT Scatterometer System," Proceedings of IEEE, Vol. 79, No. 6, June 1991, pp. 850-866

11) http://www.eorc.nasda.go.jp/ADEOS/Project/Nscat.html

12) P. Y. Deschamps, F. M. Bréon, et al., "The POLDER mission: Instrument characteristics and scientific objectives," IEEE Transactions on Geoscience and Remote Sensing, Vol. 32, 1994, pp. 598-615

13) P. Y. Deschamps, M. Herman, A. Podaire, M. Leroy, M Laporte, P. Vermande, "A Spatial Instrument for the Observation of Polarization and Directionality of Earth Reflectances: POLDER," IGARSS '90 Conference Proceedings, Washington, D. C.

14) H. Kobayashi, T. Ogawa, et al., "IMG, precursor of the high-resolution FTIR on the satellite," SPIE Proceedings, Vol. 3501, Optical Remote Sensing of the Atmosphere and Clouds, Beijing, Sept. 15-17, 1999, pp. 23-33

15) "Upper Atmosphere Monitoring with ADEOS - ILAS and RIS," EA/NIES brochure provided by Y. Sasano of NIES

16) "Ozone Layer Observation by Satellite Sensors," Proceedings of the International Workshop on Global Environment and Earth Observing Satellite Sensors, December 8-9, 1993, Tokyo, Japan

17) Y. Sasano, et al. , "ILAS and RIS for ADEOS," SPIE, Vol. 1490 , 1991, pp. 233-242

18) http://www.eorc.nasda.go.jp/ADEOS/Project/Ilas.html

19) M. Maeda, M. Ogawa, M. Sawabe, M. Hirota, H. Kunimori, "Accuracy of trajectory determination and prediction of ADEOS with RIS experiment," Proceedings of SPIE, Vol. 3218, pp. 31-39, `Laser Radar Ranging and Atmospheric Lidar Techniques,' Ulrich Schreiber; Christian Werner; Eds., Dec. 1997

20) "Retroreflector-In-Space for ADEOS: Earth-Space-Earth Laser Long-Path Absorption Measurements of Atmospheric Trace Species," Optical Remote Sensing of the Atmosphere, 1990 Technical Digest Series of the Optical Society of America, Volume 4, pp. 488-490

21) A. Minato, N. Sugimoto,, S. Sasano, "Optical Design of Cube-Corner Retroreflectors Having Curved Mirror Surfaces," Applied Optics, Vol. 31, 1992, pp. 6015-6020