Albert P. H. Goede

SCIAMACHY: Mission Objectives and Measurement Modes

Abstract SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) is a spectrometer designed to measure sunlight transmitted, reflected, and scattered by the earth’s atmosphere or surface in the ultraviolet, visible, and near-infrared wavelength region (240–2380 nm) at moderate spectral resolution (0.2–1.5 nm, λ/Δλ ≈ 1000–10 000). SCIAMACHY will measure the earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere observed in occultation. The extraterrestrial solar irradiance and lunar radiance will be determined from observations of the sun and the moon above the atmosphere. The absorption, reflection, and scattering behavior of the atmosphere and the earth’s surface is determined from comparison of earthshine radiance and solar irradiance. Inversion of the ratio of earthshine radiance and solar irradiance yields information about the amounts and distribution of important atmospheric constituents and the spectral reflecta...

SCIAMACHY—scanning imaging absorption spectrometer for atmospheric chartography

Abstract SCIAMACHY will perform global measurements of atmospheric trace gases in order to retrieve their global total column amounts as well as their stratospheric and tropospheric profiles. Aerosol abundances will be derived from observations of wavelength-dependent light scattering characteristics. Furthermore, the instrument will yield physical parameters of clouds, stratospheric temperature and pressure profiles; the latter being derived from Sun occultation measurements. SCIAMACHY observes the backscattered radiance over the wavelength range 240–2380 nm. Differential optical absorption spectrometry (DOAS) and back scattered u.v. (BUY) retrieval techniques are selected for the inversion of radiance. Ground scenes are scanned by a two-mirror scanning mechanism of high positioning accuracy. The instrument electronics, including subsystem controller and data electronics, mechanisms and thermal control electronics, allow SCIAMACHY to be operated autonomously. The instrument will be flown on the polar platform of the first European Polar Orbit Earth Observation Mission (POEM-1), now known as ENVISAT. It has been developed by the following industrial team: Dornier (prime-contractor, thermal control, instrument control); OHB (data electronics); SRON (detector modules and analogue electronics); TPD (optical unit).

Airborne heterodyne measurements of stratospheric ClO, HCl, O3, and N2O during SESAME 1 over northern Europe

Vertical distributions of ClO, HCl, N 2 O, and O 3 have been retrieved from airborne observations of pressure-broadened emission spectra in the frequency range of 620 to 690 GHz. Observations were made in February 1994 in the Arctic stratosphere above northern Europe with the Airborne Submillimeter SIS Radiometer (ASUR) during the Second European Stratospheric Arctic and Mid-latitude Experiment (SESAME) 1 campaign. ASUR is the first airborne submillimeter experiment to employ the new superconductor-insulator-superconductor (SIS) receiver technology for stratospheric ozone research. Owing to meteorological conditions, all observations were made outside the polar vortex. The retrieved volume mixing ratio (VMR) profiles show a good agreement with observations made by the submillimeter limb sounder (SLS) operated by the Jet Propulsion Laboratory (JPL) (Pasadena) and the Kern Forschungs Anlage (KFA) (Julich). A comparison between retrieved VMR profiles and profiles obtained from the SLIMCAT three-dimensional stratospheric chemistry model also shows a good agreement. Two ClO emission lines, at 649 and 686 GHz, respectively, are shown to be equally adequate lines for observation purposes. An anticorrelation has been found between the N 2 O and HCl VMR values, and also between the N 2 O and ClO VMR values. The correlations between N 2 O and HCl do not show the relatively low HCl VMR values correlated to relatively low N 2 O values as shown by Webster et al. [1994].

Nadir, limb, and occultation measurements with SCIAMACHY

Abstract The Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) is a contribution to the ENVISAT-1 satellite, which is to be launched in mid 2001. The SCIAMACHY instrument is designed to measure sunlight transmitted, reflected and scattered by the Earths atmosphere or surface simultaneously from the UV to the NIR spectral spectral region (240 – 2380 nm) in various viewing geometries. Inversion of the SCIAMACHY measurements will provide the amount and distributions of a large number of atmospheric constituents in the stratosphere and troposphere (O 3 , NO 2 , H 2 O, CO 2 , CH 4 , N 2 O, BrO, CO, O 2 , O 2 ( 1 Δ g ), NO, SO 2 , H 2 CO, (ClO,) and OClO). This paper concentrates on the characteristics of the SCIAMACHY mission. In particular, the measurement strategies for the different observational modes — nadir, limb, and both solar and lunar occultation — and their operational implementation are described.

SCIAMACHY instrument on ENVISAT-1

SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) is a contribution to the ENVISAT-1 satellite, which is to be launched in spring 2000. The SCIAMACHY instrument is designed to measure sunlight transmitted, reflected and scattered by the Earths atmosphere or surface. The instrument measures simultaneously from the UV to the NIB spectral spectral region (240 - 2380 nm). Observations are made in alternate nadir and limb viewing geometries and also for solar sunrise and lunar moonrise occultation. Inversion of the SCIAMACHY measurements will provide the following: the amount and distributions of some important trace gases O3, BrO, OClO, ClO, SO2, H2CO, NO2, CO, CO2, CH4, H2O, N2O, p, T, aerosol, and radiation flux profiles, cloud cover and cloud top height. Combination of the near simultaneous limb and nadir observations enables the tropospheric column amounts of O3, NO2, CO, CH4, H2O, N2O, SO2, and H2CO to be detected. SCIAMACHY will provide new insight into the global behavior of the troposphere and the stratosphere.

Low-noise InGaAs infrared 1.0- to 2.4-μm focal plane arrays for SCIAMACHY

SCIAMACHY has been selected for the ESA environmental satellite ENVISAT with the objective to carry out atmospheric research in the UV, VIS, and IR spectral range. The most innovative parts of the instrument are the low- noise InGaAs semiconductor focal plane arrays covering the 1.0-2.4 micrometers wavelength range. For the first time InGaAs focal plane arrays with an extended wavelength range have become space qualified. In this paper theory and measurement of the dark current and noise behavior of these detectors is presented. Each InGaAs focal plane array consists of a 1024 pixel linear photo-detecting sliver and two 512 pixel multiplexing read-out chips. Each multiplexer contains 512 individual charge transimpedance amplifier and correlated double sampling circuits. A cylindrical lens, integrated in the detector housing, focuses the light on detector in the cross-dispersion direction. The InGaAs composition of the detectors is tuned to match the required wavelength range. Measurements have been performed of the dark current and noise as function of temperature and bias voltage in order to relate their performance to theory presented in this paper. InGaAs detectors sensitive to 2400 nm wavelength achieve dark current levels as low as 20-100 fA per detector pixel area of 1.25 (DOT) 10-4 cm2 at an operating temperature of 150 K and a bias voltage of 2 mV. Lower temperatures further reduce the dark current but also decrease the quantum efficiency at long wavelengths, yielding no net gain in performance. The development programme of these SCIAMACHY detectors has been carried out by Epitaxx Inc., for and in cooperation with the Space Research Organization Netherlands.

SCIAMACHY advanced data retrieval algorithm development

Abstract The atmospheric chemistry instrument SCIAMACHY is a joint German-Dutch-Belgian contribution to the European Space Agency environmental satellite ENVISAT scheduled for launch in mid 2001. Instrument performance and calibration measurements recently carried out under thermal vacuum conditions have confirmed predicted performance. Algorithm development at SRON using the UV and visible part of the solar spectrum for ozone profile retrieval and the near infrared for carbon monoxide and methane retrieval has shown good progress. In particular, new avenues have been explored for the development of a fast operational algorithm for the retrieval of ozone profiles, including a new forward model based on perturbation theory that is faster than the current operational algorithm, coupled to a new inversion scheme with no use of a-priori ozone profile information. The near-infrared retrieval of CO and CH 4 is expected to yield higher accuracy data products based on the optimization of retrieval using micro-windows. New and advanced SCIAMACHY data products will be piloted in the Netherlands SCIAMACHY Data Centre that complements the operational ENVISAT payload data segment.

SFINX: a far-infrared limb sounding spectrometer for stratospheric trace-gas measurement (OH, HCl)

SFINX (SRONs Fabry-perot INterferometer eXperiment) consists of a 65 - 90 micrometer wavelength spectrometer based on a Fabry-Perot interferometer, and is equipped with both a conventional Ge:Ga photon detector operating at 4 K, and a novel high-temperature superconductor (HTS) bolometer detector operating at 87 K. The spectral resolution is about 8000, or 0.015 cm-1, comparable with the width of the thermal emission lines of the stratospheric species under study. Target molecules are OH, HCl, HO2, and possibly more. The SFINX instrument now under development will fly as a piggy-back instrument on a stratospheric balloon together with the MIPAS-B2 instrument of IMK/FZK (Karlsruhe, Germany), and can be regarded as a proof of concept for a satellite application. Because of its low satellite resource demands, for a satellite application a SFINX like instrument has great advantages with respect to Fourier transform spectrometers or heterodyne receivers. In particular, the HTS bolometer detector can be cooled by mechanical coolers which are presently available in space- qualified versions, thereby avoiding the use of liquid cryogen.

Scanning imaging absorption spectrometer for atmospheric cartography (SCIAMACHY) development

SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY) is a spectrometer developed for atmospheric space research, which covers the UV to near infrared spectral range, and is presently scheduled for flight on ENVISTAT-1 (1998). The principal scientific objective is the measurement of the global distribution of atmospheric trace gases, aerosol and cloud. Special emphasis is placed on the measurements in the stratosphere and the free troposphere. The current status of the instrument development is reported with details on the near infrared detectors. The predicted performance of the instrument in terms of signal to noise has reached an acceptable level in the infrared. Critical polarization issues have been identified and their solution is discussed.

GOME instrument simulation

The paper presents a detailed software simulation package for the Global Ozone Monitoring Experiment (GOME) instrument which will fly on ERS-2 in 1994. The GOME instrument is a nadir-viewing spectrometer designed for measurements of ozone and related trace gases such as NO, NO2, ClO, BrO, OClO, HCHO, SO2, O2/O4, and H2O. Examples are presented of input and output spectra and signal-to-noise calculations for normal viewing mode (nadir observations) and for sun and moon calibration mode. The GOME instrument simulating program can be used for a variety of purposes during instrument development, such as tests and calibrations, and tests of the so-called Zero-to-One processing step. The scheme could be adapted to other optical instruments.