Akihiko Kuze

Solar-occultation FTS for inclined-orbit satellite (SOFIS): scientific requirements and current status of development

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar-occultation Fourier-transform spectrometer developed by the Environment Agency of Japan (EA). SOFIS onboard the Global Change Observation Mission-Al (GCOM-Al) satellite will be put into a 650 km non-sun-synchronous orbit with an inclination angle of 69 deg. GCOM-Al is scheduled to be launched in spring 2006. SOFIS is the successor of the Improved Limb Atmospheric Spectrometer-II (ILAS-II), which with travel onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS will measure vertical profiles of atmospheric constituents with 0.2 cm-1 spectral resolution at 3 - 13 micrometer with 1 km vertical resolution. The scientific objective of SOFIS is to measure global vertical distributions of O3, N2O, CH4, CO2, H2O, HNO3, NO2, aerosols, CFC-11, CFC-12, and ClONO2. SOFIS uses a double-pass dual-pendulum type Fourier transform spectrometer (FTS) and a diode laser sampling system to reduce the size and weight of the apparatus. Two photovoltaic (PV) HgCdTe (MCT) detectors and a pulse-tube cooler will provide high linearity and low-noise performance. SOFIS also has a visible (O2 A band) grating spectrometer for pressure and temperature retrieval and a sun- edge sensor for detecting the tangent height position. This paper describes the characteristics of SOFIS and test results of laboratory models of the FTS and the detector.

Feasibility study on solar occultation with a compact FTIR

A feasibility study for the solar occultation observation from space has been carried out. An ordinary Michelson type Fourier transform spectrometer with 1 cm-1 resolution and 10 Hz rapid sampling showed best feasibility by the trade offs among the sensitivity and resource consideration. For the low- cost and quick development, it is assumed to use design similar to a commercial laboratory model. By using 200 K TE cooled PC-MCT detector, it showed least resource requirement and the SNR greater than 150 over 800 to 3300 cm-1. By using 80 K MCT, it is possible to achieve the SNR greater than 500 can be achieved with more resources for weight and power.

Conceptual design of solar occultation FTS for Inclined-Orbit Satellite (SOFIS) on GCOM-A1

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer developed by the Environmental Agency of Japan, and onboard the Global Change Observation Mission-AI (GCOM- A1) satellite. GCOM-AI will be placed in a 650 km non-sun- synchronous orbit in 2006, with an inclination angle of 69 deg. SOFIS is the successor of the Improved Limb Atmospheric Spectrometer-II, which is onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS measures the vertical profile of the atmospheric constituents with 0.2 cm-1 spectral resolution at 3 - 13 micrometers and 1 km vertical-resolutions. The target of SOFIS measurements is a global distribution of O3, HNO3, NO2, N2O, CH4, H2O, CO2, CFC-11, CFC-12, ClONO2, aerosol extinction, atmospheric pressure and temperature. SOFIS uses a double-pass flexible blade Fourier transform spectrometer (FTS) and a diode laser sampling system to reduce the size and weight of the apparatus. Two photovoltaic HgCdTe detectors and a pulse-tube cooler will provide high linearity and low-noise performance. SOFIS also has a visible (O2 A-band) grating spectrometer for pressure and temperature retrieval and a sun-edge sensor for detecting the tangent height position. This paper describes the conceptual design of the instrument and examines the test results of laboratory models of the FTS and the detector.

Feasibility study for spaceborne compact FTS and preliminary test results of laboratory model

A laboratory model of the space borne compact FTS was manufactured and tested. This type of compact FTS with medium spectral resolution (approximately 0.8 cm-1) and high spectral scan rate (approximately 10 Hz) is suitable for the observation of the vertical distribution of atmospheric constituents, especially for the observation of solar occultation. The rapid vertical velocity of tangent points requires a high spectral scan rate of the instrument. One of the candidates of platforms is the International Space Station (ISS). The results of a sensitivity study show that a moderate spectral resolution of approximately 1 cm-1 is sufficient for measuring vertical distributions of the trace gases with a measurement error less than 10%. The laboratory model is based on the Bomem/MR series with balanced rotary scan action and a frictionless flex blade at the center of rotation. For data sampling, a diode laser is utilized instead of a He-Ne gas laser. This technique provides the compactness and longevity in FTS needed for the satellite borne system. For this instrument, a vibrational environment test was conducted and it was proved to be well-balanced and to be a stable structure with a high resonance frequency. This paper also proposes a space borne interferometer.

Ozone dynamics ultraviolet spectrometer (ODUS)

The Ozone Dynamics Ultraviolet Spectrometer (ODUS) is a satellite-borne, nadir-looking ultraviolet spectrometer for measuring total ozone amount. It will be launched in 2005 onboard Japanese earth observation satellite GCOM-A1. The ODUS instrument measures continuous spectrum from 306 to 420 nm with 0.5 nm spectral resolution and 20 km spatial resolution, using an Ebert-type polychromator and a one-dimensional silicon CMOS array detector, which will improve the accuracy of the retrieved total ozone amount. We have completed the conceptual design of system, and manufactured and tested the laboratory model of the detector and the optical assembly. We have succeeded in developing a detector with sufficient sensitivity and a polychromator with little stray light. We have also confirmed the optical performance and evaluated the detailed wavelength structure of the instrument function. This paper presents an overview of the ODUS instrument, the summary of the evaluation results of the laboratory models.

Measurement of greenhouse gases from space with a SWIR FTS

Considering global increase in greenhouse-gases, observation and monitoring of the earths atmosphere with space-borne instruments are essential. Satellite measurement offers the advantage of global and long-term monitoring. In the short wave infrared (SWIR) region of 1.5-1.9 micrometers , major greenhouse gases (carbon dioxide (CO2), water vapor (H2O), and methane (CH4)) have absorption spectra of moderate strength without interference by other molecule absorption. In addition, we can use the un-cooled detector for this wavelength region. Two different types of observation geometry will be discussed; one is nadir-looking with sun glint light source for the column amount retrieval and the other is limb-looking with scattered light source for the vertical profile retrieval. We propose the four- ports Fourier transform spectrometer (FTS) for this application. One input port is for nadir-looking measurements and the other input port is for limb-looking measurements. One output port is used for greenhouse gases measurements and the other port is used for the oxygen (O2) absorption spectra measurement for the optical path length calibration. The instrumentation of the FTS, retrieval algorithm and expected performance are discussed, and ground test results are also presented.

Instrumentation and laboratory model test results of solar occultation FTS for inclined-orbit satellite (SOFIS) on GCOM-A1

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer (FTS), developed by the Ministry of the Environment (MOE) of Japan, that will be onboard the Global Change Observation Mission-A1 satellite. We describe the performance test results of the laboratory model and present the instrument and engineering model test results.

Specifications of GCOM-A1/ODUS

UV spectrometers onboard satellites have provided trend data of total O3 for more than two decades. These data have shown the validity of satellite measurements. However, for next-generation observation and to monitor the recent O3 depletion accurately, a high-fidelity spectrometer with high signal to noise ratio (SNR) is essential. For this purpose, the Ozone Dynamics UV Spectrometer (ODUS) has been designed to have higher spectral and spatial resolutions and wide spectral range. It will be launched on the Global Change Observation Mission (GCOM)-A1 satellite in 2006. ODUS covers back- scattered light from 306 to 420 nm with 0.5 nm spectral and 20 km spatial resolutions using a Fastie-Ebert type polychromator and a one-dimensional UV Si-CMOS array detector. The array detector is designed and manufactured specially for ODUS. It has different size pixels and 234 on-chip CMOS amplifiers, which are tuned for each spectral radiance level. ODUS is a nadir-look mapping spectrometer with a mechanical scatter, which can acquire global data in one day. It is expected to provide information about total O3, SO2, NO2, BrO, OClO, H2CO, surface albedo, and aerosol.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Requirement definition study for GCOM-A1/ODUS instrument

This paper defines scientific requirements for the Ozone Dynamics Ultraviolet Spectrometer (ODUS). ODUS is a cross- track scanning spectrometer like Total Ozone Mapping Spectrometer (TOMS) developed by NASA. This instrument is planned to be flown on the Global Change Observation Mission (GCOM)-A1 satellite. ODUS measures solar ultraviolet radiation backscattered from the Earths atmosphere. This study examines the necessity and feasibility of retrieval algorithms for total ozone, volcanic sulphur dioxide (SO2), nitrogen dioxide (NO2) and several other constituents related to ozone chemistry and summarizes requirement definitions for specifications of the ODUS instrument. Finally, we review the conformance of the development policy for retrieval algorithms with the current specifications of the ODUS instrument.

Trade-off studies on ODUS spectrograph design

ODUS (Ozone Dynamics Ultraviolet Spectrometer) on the GCOM (Global Change Observation Mission)-A1 mission will measure the ozone, SO2, NO2 and other trace constituents both in the stratosphere and in the troposphere through the backscatter ultraviolet (BUV) technique from 306 nm to 420 nm. In the present paper, the design concepts of the ODUS were clarified and a trade-off study among various spectrometer types was done. Since GCOM-A1 will have a non-sun-synchronous orbit, the thermal condition during a recurrent cycle will be more variable than that of a sun-synchronous orbit. Therefore, misalignment caused by thermal stress distortion was expected to be the most critical matter. As a result, a simple conventional Ebert type spectrometer was employed. However astigmatism is a matter of serious concern for the Ebert type spectrometer, because it leads to a significant loss of the input photon flux caused by the image extension of the entrance slit in the direction of detector height. The optimal slit height was determined by the trade-off study between high throughput and the image distortion due to astigmatism. As a detector, a linear photodiode array was employed for ODUS. As the detector is custom made, the shape and the arrangement of each photodiode pixel can be modified by changing the mask design. We optimized the detector height for each photodiode pixel to maximize the SN ratio by calculating the instrument function. According to the above process, the detector was newly fabricated with a dramatic change of the mask design. The new detector was combined with the previously fabricated laboratory model spectrometer. We successfully obtained atmospheric scatter data on the ground with a signal to noise ratio of 350 at the wavelength of around 400 nm.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.