Following the approval of the proposed project by DLR, data sets necessary to carry out the projects will be provided to the selected Principal Investigators free of charge. For proposals requesting large data volumes, data provision will be negotiated on a case-by-case basis prior to the acceptance of the proposal.

All X-SAR/SRTM data will be distributed by DLR's DFD (Deutsches Fernerkundungsdatenzentrum / German Remote Sensing Data Center), except for data over Italian territory, which will be provided by ASI.

The X-band ITED-Level 2 data is intended to be made available starting in summer of the year 2000, the C-band ITED-Level-1 and -2 data should be ready for release by the summer of 2001. The progress of the data preparation may be monitored via Internet.

The SIR-C ITED-2 data will be available for the national territory of Germany, the USA and to-be-determined areas for jointly agreed scientific investigations subject to NASA-NGA data-use-guidelines. SIR-C ITED-1 products will be available globally. X-SAR elevation products will be available globally.

It should be noted that all X-SAR/SRTM data will be catalogued and made available to other users. No data supplied in the framework of this Announcement of Opportunity may be transferred, sold or given to third parties other than approved Co-Investigators without the written authorization of DLR.

Prior to the usage of the data the Principle Investigator will have to sign an agreement "Terms and Conditons of Usage of SRTM data" which reflects the legal arrangements agreed upon in the NASA-DLR SRTM and X-SAR MoU concerning data usage.

The progress and accomplishments of the projects selected through this Announcement will be monitored by DLR. All accepted Principal Investigators will be required to submit periodic progress reports describing the status of their work. At the end of the project, a final report in accordance with a given format is mandatory.

Principal Investigators must submit their final reports to DLR in German or English, and present their results at the following milestone workshops organized by DLR: I. Calibration/Validation one year post-mission, II. Scientific Applications two years post-mission, III. Commercialisation three years post-mission (or earlier). They may also be asked to present results or parts of their results at special workshops organized by DLR and NASA.

In order to make research findings available to other data users, all Principal Investigators must provide their project results in a common digital format, which is going to be defined by DLR.

In addition to free access to SRTM data, DLR may provide funding to some of the accepted projects of German Principal Investigators.

The DLR Earth Observation Utilization Program will fund a limited number of the selected projects covering topics from calibration/validation science, concerning interferometric methods and the demonstration of commercial applications. Accepted German PIs may apply for DLR funding within the normal application procedure. However, since funding resources of DLR are limited, you may consider to consult other funding agencies, which may support AO-associated projects within the framework of their own programs.

With its performance and functional capabilities, the two 1994 radar shuttle missions SIR-C / X-SAR have set new standards for imaging microwave remote sensing sensors from space. They have also successfully demonstrated repeat pass interferometry in all three frequencies (X-, C-, L-band) with a 1-day repeat as well as a 6-month repeat orbit. The well known problem with repeat orbit interferometry is the temporal target decorrelation, unsuitable baselines and different squint angles for the two passes to be processed. Therefore, for the third mission of SIR-C / X-SAR, a single-pass interferometry system with a second receive antenna is proposed to generate a topographic map of all land surfaces between +60⁰ and -58⁰ latitude. The requirement for the topographic mission is to map about 80% of the entire Earthís landmass. The radar instruments will image all land surfaces in ascending as well as descending passes to meet the performance requirements especially for mountainous areas and to minimize the unwanted effects of layover and radar shadow.

Until today, only limited digital topographic maps are available. They vary in geometric resolution and datum and are only partly available to the scientific public. While the only existing global digital dataset has a horizontal resolution of 1 km and a vertical height resolution of 100 m, SRTM will render a 30 m horizontal and 10 m vertical height resolution in the C-band and even a 6 m vertical resolution in the X-band.

A two-frequency single-pass interferometric SAR is configured by simultaneously operating two sets of radar antennas, one with transmit/receive and one with receive-only antennas separated by a baseline length of 60 m and two receiver channels. X-SARís 12 meter long and 40 centimeter wide main antenna for transmit and receive (channel one) is mounted directly to a tiltable part of the SIR-C antenna truss structure in the Shuttle cargo bay.The second receive-only antenna is 6 meter long and is mounted together with the second 8 meter long C-band antenna (channel 2) on a 60 meter long, deployable, stiff boom structure perpendicular to the velocity direction of the space Shuttle to create the baseline. X-SAR is not capable of operating in a ScanSAR mode like SIR-C which would allow complete coverage of the Earth during an 11-12 day Space Shuttle mission, but it will operate in a high resolution mode with a swath width of about 50 km placed inside the SIR-C ScanSAR swath at an angle of 52 degrees off nadir.

The principle coverage pattern for the X-SAR and SIR-C systems is shown in the figures below. For more detailled information refer to the following web-pages:

Processing, archiving and distribution of all X-SAR/SRTM data will be performed at DLRís DFD (German Remote Sensing Data Center), except for the area of Italy. The processing comprises the standard SAR processing including phase unwrapping, DEM generation and data mosaicking. Already during the mission, a considerably large amount of X-SAR data will be transmitted directly to NASAís Jet Propulsion Laboratory (JPL). These data will be used for system checks, system verification, calibration and product validation for selected areas. Additionally, a certain amount of data will be sent to DFD during the mission via high speed data networks. These data are open for public relations activities during the mission, general mission support, for checking of the processing facilities and for the cooperating calibration/validation teams.

Upon mission completion, all data will be copied to special D2-cassette tapes at JPL and transported to DFD. After this, the screening of the whole data set will take place. This process is the main task of the commissioning phase when all raw data will be archived, raw data statistics derived, calibration performed and automatic high throughput processing prepared. This phase will last at least 6 months. During this phase, selected sites of calibration/validation proposals will be processed according to a priority schedule defined pre-mission by DLR (see below).

After the initial data screening, the standard processing will begin. This phase will last until all X-SAR data have been processed to digital elevation models and images, approximately two years. The products will be archived in the DFD robot archive and made available to the user via a WWW-customer and user interface. On the website the current processing status of the DEMs will be shown.

The priority scheduling will take into account special needs for fast product delivery and calibration/validation support. The DFD will make available the X-SAR/SRTM products following an optimized schedule which will be set up after the evaluation of the AO proposals. The schedule may be revised after the commissioning phase.

The data orders will be accepted at at DFDís multi-mission user interface (MUIS) within the WWW-home page of the DFD. The user will be asked for his identification. After validation he may specify the requested area (by coordinates or by map browser) and the desired product type (clickable scroll bar items). The system checks for the information given and returns the estimated delivery time.

SRTM-products will be distributed either by CD-ROM or electronically (preferred) together with accompanying product information.

The following priority levels will be applied:

Proposals are invited which support the calibration and validation of the X-SAR interferometric data products by providing accurate terrain height information either as ground control points, kinematic GPS tracks or reference DEMs. Although proposals are sought for both calibration and validation, contributions for the latter are particularly welcome. However, depending on the geographic distribution of the available ground truth information the project will decide on whether to use the data for calibration or validation. The intended approach for calibration and validation is outlined in the following sections.

4.1.1 Calibration concept

The X-SAR system calibration includes two parts: the radiometric and the interferometric calibration. The high radiometric accuracy of the X-SAR during SRL-1/2 will be verified using ground receivers and rain forest data for antenna pattern measurements, and corner reflectors for absolute calibration. Here, we concentrate on interferometric calibration including X-SAR instrument phase calibration, and InSAR imaging geometry calibration.

The most critical parts of the X-SAR electronics are the boom cables, where high temperature variations between -50^oC and -10^oC are expected. Another problematic section is the path from the six panels of the secondary antenna to the combiner box including the phase shifters for beam steering. Electronic steering effectively tilts the antenna aperture and results in a shift of the phase center. Corrections require a precise knowledge of the behaviour of these phase shifters.

Instrument phase calibration includes three major parts:

The shuttleís boom will provide a mechanical fixed baseline that will enable an interferometric imaging from parallel orbits. Nonetheless, possible boom dynamics, caused by the shuttleís orbit maintenance maneuvers, gravitational effects, and boom twisting due to thermal effects may cause changes of the attitude of the secondary antenna and, therefore, may vary the interferometric baseline. The use of the so-called Attitude and Orbit Determination Avionics (AODA) system, that includes GPS receivers, star trackers, inertial reference units, optical trackers, and electronic distance meters, will allow an accurate relative measurement of the interferometric baseline vector. It will further provide antenna attitudes, orbital state vectors, and the time-base for both radar systems.

However, systematic errors in the AODA measurements due to offsets in the mounting of the AODA instruments and thermal variations during the flight may affect the measurement accuracy of both the baseline length and tilt angle. A calibration of this measurements can be performed by evaluating data sets acquired over areas with well-known height (e.g., ocean or reference data provided by Principal Investigators). Additionally, for the radiometric calibration, corner reflectors deployed at calibration test sites will be used to estimate the range delay and a possible time-tag offset. A differential range delay that may occur between the two interferometric channels will be estimated during image co-registration.

4.1.2 Validation concept

The validation of the interferometrically (InSAR) derived DEMs will be performed in two steps. A project internal validation will be carried out during the commissioning phase (ending 6 months after the mission) by a DLR team consisting of colleagues from SAR/InSAR processing and calibration. The project validation will concentrate on selected sites and will include a cross-validation with C-band results.

Furthermore, we particularly invite investigators to propose validation experiments for the standard SRTM products. PIís will receive InSAR DEMs and use their own reference data for validation. InSAR DEM validation has to consider the type and height of vegetation cover and the frequency dependent canopy penetration. Statistical analyses will be performed and compared with the annotated error map.

4.1.3 Proposals for calibration and validation

Proposals, which aim to contribute to the calibration and validation process, will have to indicate clearly the:

Reference data should be in WGS84 (horizontal and vertical datum). Source and accuracy of the reference data have to be clearly specified. Reference data could be:

A non-exclusive list of examples for scientific proposals spans the following areas:

4.2.1 Radar backscattering and penetration depth

Enhancement of knowledge about radar backscattering and penetration depth. Since X- and C-band radar signals only partly penetrate through vegetation, the interferometric DEMs represent the terrain height plus an unknown vegetation height (see also 4.1.2). Investigation of the location of the scattering medium for a variety of surface types is, therefore, a desirable information to determine the true terrain elevation.

4.2.2 Local incidence angle correction with respect to surface cover

Radar backscattering is differently depending on the incidence angle for various surface covers or roughness heights. Since the local incidence angle varies with topography, a valid angle correction (e.g., for classification or sensor synthesis) is only possible if the relief and the surface-specific backscatter characteristics are known. Proposals should address representative surface or vegetation types to establish a catalogue.

4.2.3 Synergistic use of different sensor systems (and GIS)

Digital Elevation Models are a pre-requisite for geo-coded satellite images and correct terrain effects in radar scenes. Since availability of DEMís has been limited in the past, development of synergistic analysis techniques for various microwave and optical remote sensing images in areas of (high) relief has only been poorly developed. Proposals should specify why synergistic sensor evaluation promises advantages and how the issue of merging will be approached.

4.2.4 Support of geoscientific research in areas of limited cartographic coverage

Proposals shall list restrictions or difficulties due to limitations of available topographic information and clearly specify the geoscientific advances which are to be expected through the use of the SRTM Digital Elevation Models.

4.2.5 Update of topographic models for climate models and application of vegetation height

The scientific advancement due to the increased geometric resolution using SRTMís elevation model shall be demonstrated for specific and well-defined applications, e.g., climate or watershed models. Alternatively, innovative use of the "top-of-the-canopy" elevation model shall be developed.

The development of operational and commercial applications of SRTM data is of particular interest to the German Earth Oberservation Programme. It will lead to the expansion of applications and the expansion of the market for value-added services.

Proposals are expected from or in close cooperation with the service industry or value-adding companies.

Commercial applications related to SRTM Digital Elevation Models are for example

Proposals are also sought which address research and development activities required in support of future commercial utilization of SRTM data products. Relevant information may be derived from SRTM data alone or in conjunction with other data sources. Such proposals may also include the definition of new products or algorithms required for the development of such applications.

Candidates should define the objectives, scope and implementation of their projects as accurately as possible along with a potential transition into market-oriented services. The implementation plan should also indicate the ways and means necessary for attaining such objectives.

Information of a proprietary nature contained in any proposal will be used by DLR for evaluation purposes only. Should any proposer out of Area III wish the details of the proposal other than the title to be considered as confidential during the course of the project, he should indicate this in the proposal. Nevertheless the PI will have to provide the regular progress reports to DLR and present his final results. The final report will be published.

Proposals have to be submitted electronically in WORD 6.0 format to:

Any deviations from the above mentioned format need to be approved by DLR prior to submission of the proposal.

The submission deadline is November 30, 1998 at midnight and no proposal received after the deadline will be accepted.

DLR may decide to select only a portion of the proposer's investigation, in which case the investigator will be given the opportunity to accept or decline such partial acceptance.

The proposal should be submitted by the investigator, or official of the investigator's organisation, who is authorised to commit the organisation to the contents of the proposal.

The proposal shall be composed of six components.

Proposals received in response to this Announcement of Opportunity will be reviewed by panels composed of:

Proposals will be rejected where results are not timely. DLR may propose adjustments to milestones to achieve mission goals.

The following criteria will be used in the evaluation process:

Following notification, the selected Principal Investigators, will have to

In some cases the Principal Investigator will be required to amend his proposal in order to meet the acceptance criteria and in accordance with the remarks expressed by the evaluators.

A briefing meeting for selected Principal Investigators will be held in spring of 1999.