GISdevelopment.net ---> AARS ---> ACRS 1989 ---> Environment ROSIS - An imaging spectrometer enviromental research Heinz van der Piepen Institute for Optoelectronic, DFVLR , D-8031 Oberpfaffenhofen, FRG Roland Doerffer Institute for Physics, GKSS, D-2054 Geesthacht, FRG. Bernd Kunkel Space Systems Group, MBB, D-8012 Ottobrunn, FRG Abstract The Reflective optics system imaging spectrometer ( ROSIS ) is a compact programmable imaging spectrometer based on a CCD matrix detector array . The instruction has been designed specially for the monitoring for the of water color and of natural chlorophyll fluorescence in order to quantitatively derive pigments suspended matter and yellow substance distributions in the marine environment how ever its high spectral resolution of £ 5 nm also permits many new air borne new application in vegetation monitoring and in atmospheric physics an air borne prototype IS ROSIS IS jointly developed at present by MBB GKSS and DFVLR the instrument concept the scope of applications and the relationship to ESA earth observation programme and to NASA earth observation system is discussed. Imaging spectroscopy The future observation system by NASA and the earth observation programme by ESA rely to a large extent on the imaging spectrometers like the high resolution imaging spectrometer the moderate resolution imaging spectrometer or the medium resolution imaging spectrometer in addition to other operational sensors these are expect to largely improve the monitoring capabilities for climatology and environment studies in regard to ocean land and atmospheric parameters. The main advantage of imaging spectrometers in comparison to conventional optional mechanical multi spectral scanners is the availability of a large number of narrow band width spectral channel combined with the positively of an applications specific selection of a few channels for data recording or transmission this permits the use of a single for a variety of monitoring tasks sensor alternatives focus instead on either medium of high geometric resolution (HIRIS, HRIS). The Narrow band width channels permit a detailed analysis of spectral fine structures which are present in many signatures related to marine biology pigment fluorescence water pollution vegetation stress land use geology atmospheric absorption features etc. As a result these sensors will permit an essential improvement of data interpretation for environmental monitoring. In preparation of NASA and ESA future space programmers a few air borne prototypes of such sensors have been developed and used during the past few years Typical examples are the air borne imaging spectrometer from the U.S jet propulsion Laboratory or the Fluorescence line manager from the Canadian Department of Fishers and oceans while the former was designed mainly for the monitoring of mineralogical features the design driver for the latter was based on earlier experience with modern CCD technology a new sensor for water color monitoring from space was studied during 1986/87 by the company MBB on observation mission with ESA's European Retrievable Carrier an air borne prototype of this under construction the instrument conception its future applications are discussed in the following sections . ROSIS Cooperation agreement Based on the EURECA / ROSIS experience an agreement between the organizations GKSSS MBB and DFVLR was signed in 1987 with the aim to develop jointly an aircraft prototype of ROSIS .In order to meet future requirements in regard to ESA's polar platform missions there aircrafts version was to be developed as closely as possible to the spacecraft version studied already before. And after through tests in to laboratory the instrument will be ready for the first flight tests in early 1990. Optical system In order to meet the stringent radiometric requirements of a water color florescence sensor throughout the relevant spectral range the optical system incorporates reflectance components only (Figure 1): The image on ground is relayed through a baffle via a lift mirror the purpose of which is to shift the scan line either forward or aft for sun glint avoidance, onto the two telescope mirrors, which focus the image on to the entrance slit of the spectrometer (the entrance slit represents the actual scan line on ground by cutting off the rest FOV); the focused scan line image is expanded and paralcllized through a collimator system (two spherical mirrors) for dispersion by means of a reflective grating (bottom of the housing); the collimating system (using again the same spherical mirrors) subsequently focuses the beam via a small deflection mirror onto the CCD detector (top of housing); the trigger and read-out electronics is arranged on top of the array so as to avoid long connections The front-end tilt mirror also serves as a means to reflect diffuse sun light into the system for calibration purposes(the reverse slide is covered by a diffuser).Further more, the same mirror is used in an intermediate position as shutter to enable dark current measurements. The off-axis system compensates partially for the slit curvature in the focal plane. The optical performance data are summarized in Table1. Figure 1. ROSIS optical scheme. Dectator array A matrix detector array of the type Thomson CSF model THX 31156 is incorporated in to the design (Table2).Thisallows1024 picture elements to be used across the scan perpendicular to the flight direction 85 spectral channel corresponding to the spectral range from 430 to 850 nm can be used in the spectral mode. all the other detector elements on the elements on the array are masked or used as intermediate storage. However since the above mentioned detector will become only available later the present ROSIS instrument will be temporarily operated with the detector model TH 7884 which permits the use of only 500 detector elements across the scan line this can be mounted either off axis for tests of the system or alternatively in Table 1. ROSIS optical performance data Total FOV................................................................. ±16 degrees IFOV ........................................................................ 0.56 mrad F Number ................................................................ 3.6 Distortion ................................................................ £ 2 % Grating constant ..................................................... n = 55 Blaze angle ............................................................ 1.01 degrees Spectral angle ....................................................... 430 - 860 nm Spectral range ...................................................... 5 nm / detector element Tilt ...................................................................... ± 20 degrees Table 2. ROSIS detector array Present Type ............................................................... Thomson CSF TH 7884 Lines / Columns ............................................... 512 X 500 Element size .................................................... 23.5 x 18.5 mm Dynamic range ................................................ 3300 :1 operation mode ............................................... frame transfer Future Type ............................................................... Thomson CSF THX 31156 Lines / Columns ............................................... 1024 X 1024 Element size .................................................... 19.0 x 19.0 mm Dynamic range ................................................ 5000 : 1 operation mode ............................................... frame transfer the center for flight operations with FOV of 16 degrees this detector will be replaced once the large one will become commercially available . Operation modes Similar to the FLI the air borne ROSIS can be operated either in the spatial or alternatively in the spectral mode (Table 3). The spatial mode allows the full geometric resolution to be recorded in up to 32spectral channels .the spatial mode allows all 85 spectral channels to be recorded simultaneously at a reduced spatial resolution the center wave length can be adjusted electronically in 1 mm steps. Data recording The control of ROSIS, the real-time quick look and the recording of data is done by means of a multi processors based VME bus system using OS/9 as real time operating system all memories on processor and inter face modules are dual-ported. Table 3. Rosis operation modes Imaging mode: 500 pixel across track ( with detector TH 7884 any of 65 wavelength selectable upon command recording of up to 32 selected channels. Spectral mode: 85 adjacent spectral channels ( 430 850 nm) every third pixel or across track. The data from ROSIS are transferred in to system as a block of one frame with up to 16 k 12 bit words. data are accepted from the aircraft inertial navigation system and from other instruments via an ancillary data inter face processor the final frame is built up in the main memory and then transformation to the disc controller which packs the information and writes it on the storage medium this will be a 51 /4 erasable will once optical disc with 1 GB storage capacity. The control processor checks the dynamic range of the radiance data and the environmental of the instrument it allows the operator to display the numeric or graphic form and to program the sampling mode adjustment a protocol of all actions is recorded on floppy disc the quick look image processor with color display provides the operator with a continuously updated image of the data. The data rate is at present maximum 85 frames per second with 2.2 MB/s. Future developments After tests flights to be performed by GKSS and DFVLR it is a planned to incorporate a wider user community in to the ROSIS data and application by means of an extensive flight programme. The present aircraft prototype of ROSIS will eventually be modified as indicated with the larger detector array so as to permit imaging of the full 32 degree FOV for which the optical system has been designed further developments may include an extension of the special range in to the short wave infrared so to be compactable with sensors like the thematic mapped or similar. In regard to space flights further studies are presently performed so as investigate in more detail the possibilities of applying the ROSIS concept to the requirements of MERIS and MODIS T incorporated in ESA EOP and NASA EOS as part of the Columns space programmed The rapidly increasing demand for environmental monitoring may also lead to a combined mission for monitoring the atmosphere plus and the coastal environmental vegetation stress water pollution and Biomass through during a period after NASA Upper Atmospheric research Satellite Mission and prior to the EOP /EOS programme i.e in the middle of the next decade investigations are taking asoas the determine how ROSIS could be modified to include the ultra spectral range for measuring solar back scattered radiation around nadir. Applications Monitoring of the water color fluorescence permits applications in the fields of marine biology and ecology water pollution and sediment transport citatory and monitoring of dynamic features. It is expected that the narrow spectral bands of ROSIS in combination with the programmable channel selection bands of ROSIS in water color monitoring in parameters in case II waters where the presence of components such as yellow substance or sediments restrict the use of color ratios fore a quantities interpretation of spectral . The possibility to adapt the spectral channels to the pigments of different populations will improve the sensitivity and specify of the system for monitoring also exceptional restricts blooms by means of color ratios or by inverse modeling of spectral . In additions it will permit a precise selection of several atmosphere correction channels for the aerosol determination as well as suitable channels for establishing a base for an evaluations of the fluorescence signal. Future land applications in context with NASA EOS will include especially the advanced monitoring to tropical rain forest vegetation index stress plant diseases and land use. it is expected that the high spectral resolution will also permit an analysis of the red edge shift of the pant albedo associated with stress features . The precise positioning of narrow band channels is expected to open addition measurements also in the field of atmospheric physics which sofar could be dealt with if at all only with active optical or micro wave sensors. These aspects include Cloud height atmospheric pressure determination by comparative analysis of radiances originating from the surface and cloud tops. Optical depth of clouds and droplet size determination by means of comparison of different liquid water absorption bands. Water vapour column content through a comparison of relative differences of radiance ratios with in out side water vapour rotation bands. acrosol type and concentration determination from radiances especially in the near infrared region. Acknowledgements The authors wish to express their particular acknowledgements to Prof..H. GRABI MPI, Mr. W. Cordes and DR. J. FischeR, GKSS, Dr. D. Beran, MR. M.Mooshuber Mr. W.W. Schrooder, DFLVIR as well as to the MBB team (Mr. F. Blechinger, DR. R. Buschner, MR. Herbig, DR. R. Lutz, MR. D. Vichmann and MR. H. Wolter, MR. R.Ziegler) for their effort and dedications in the planning developing and test of the prototype of ROSIS. References NASA, "MODIS instrument panel report" Earth observation system VOL. 11b (1986). NASA "HIRIS instrument panel report" Earth obdservation system VOL HC (1987). ESA, "Imaging spectrometry fror land applications," Proc. of an workshop held at Frascati, 19-21 APRIL 1988, ESA SP-1101, OCT.1988. C.O. Davis, "Future U.S. ocean coor missions - OCI, MODIS, HIRIS," in Occanpography from space, J.F.R. Gower ed., Advances in space research 7 (2), 3-9 (1987) A.B. Hollinger, L.H. Gray J.F.R. Gower and H,R. Edwl, "The fluorescence line imager: An imaging spectrometer for ocean and land remote sensing" Proc. SPIE. 834, 2-11(1987). MBB "Chlorphlyll mapping of the ocean by means of detector array sensors" (Feasibility and definition study) BMFT contract No. 01 QS 8508 8, Final Report (1988). GKSS, "The use of chlorophyll fluorescence measurements from space for separating constituments water," ESA contract No. RFQ 3-5059 / 84 / NL / MD, Vol I (Summary Report) and vol II (Appendices (1986). R. Doerffer V. Amann and H van der Piepen, "Remote sensing of exceptional plankton blooms, "Proc. ICES Special Meeting on causes, Dynamic and Effects of exceptional Marine Blooms and related evrnts, Copenhagen. 1984