Ready-to-use GIS information from remotely sensed data G. Sylos Labini*, S. Samarelli*, G. Pasquariello^ G. Nico*, A. Refice* & J. Bequignon ' Planetek Italia, Tecnopolis, 70010 Valenzano, Bari, Italy * CNR-IESI, Bari, Italy * INFM, Dipartimento Interateneo di Fisica, Bari, Italy * Remote Sensing Department, Application directorate, ESRIN, Frascati (Roma), Italy Abstract data are not suitable for direct use by the GIS community. A wide variety of users, ranging from urban planners to Earth resource managers or insurance brokers, have been managing territorial information in Geographical Information Systems. They want to get relevant and updated information, ready to be inserted into their systems. In order to fulfil these requirements, the relevant information must befirstextracted from the radiometric data gathered by the satellite sensors. Information must then be made available in a suitable format. A study has been performed to address the aspect of the realisation of GIS products, generated from remotely sensed data, and tailored to be closer to the end users needs. In a study performed for the European Space Agency, Planetek investigated whether new, GIS-oriented products, derived from ERS-1 and ERS-2 Synthetic Aperture Radar () data, could be provided to these user communities. The study has been focused on two key issues: an identification of the kind of product required by end users, and a specification of an appropriate format for product distribution. In order to validate the concept proposed in this study, it has been decided to perform a detailed study of one product. As sample product we selected the flood. The result is a vector of the flooded zones, which is of immediate usage forfinalusers.
262 GIS Technologies and their Environmental Applications 1 Introduction Using data produced from Earth Observation missions into GIS database development can be considered one of the major operational applications of remotely sensed data. sensors, such as the LANDSAT Thematic Mapper or the SPOT Resolution Visible, have been extensively used to produce geographic data to be introduced into a GIS. However, data are still lacking behind in operational applications, due to a number of reasons. Firstly, the informational content of a image is not as directly interpretable as that of an optical one. Although many studies have been done on this subject, and many aspects of the interaction between a microwave image and the earth surface is by now well known, a unique and agreed approach to the integration of data into Geographical Information Systems does not exist as yet. A image also presents peculiar distortions which are to be properly treated in order to get relevant information. 2 The "GIS & Remote Sensing" project In order to investigate these aspects of the use of remotely sensed data for integration into GIS environments, an extended study has been performed by Planetek, under ESA funding, which considered a series of potential GIS applications which could receive benefits from the use of remotely sensed data. A series of ranking criteria have been established to rate both technical application requirements that a possible GIS, derived implementation should possess to be competitive, and market characteristics of such a product. Such a set of criteria, discussed and approved by ESA, has been carried out bearing in mind ESA and user requirements and data availability [ 1 ]. 2.1 data integration into GIS For several applications, an extensive although not exhaustive review has been performed. It gives indications about some questions related to the general problem of data integration into GIS. In particular, it has been considered which is the accuracy reachable in eveiy field by the use of data. Also, the main problems in each particular application have been pinpointed, and, whenever possible, solutions are suggested. These considerations led to assess a general degree of feasibility for each kind of product.
GIS Technologies and their Environmental Applications 263 The application fields considered involved sea ice and snow monitoring, forestry, agriculture, hydrology, geology, disaster management and risk assessment, and coastal area study. Also, a strong emphasis was given to the use of innovative techniques such as interferometry. Given the peculiarity of most interferometric applications, a separate part of the study was devoted completely to a critical assessment of the main fields of application of this kind of data, i.e. topography, differential topography (applied to glacier movement and landslide ping), and classification of the coherence (for land use and flood ping). The selected applications of data for each fields are reported in Table 1, together with some parameters of evaluation of theneffectiveness, such as the necessary source data, the characteristic time interval for the application, the ancillary data needed to calibrate or match the data, the relative degree of accuracy which is possible to reach in that application (with respect to the field needs and to the state of the ait of research in that field), and its degree of automation (considered as a function of the degree of experience required in the technical personnel involved in the product generation). A more quantitative evaluation of each application has also been given, based on a series of criteria such as application maturity (intended as the level of knowledge reached in that field by the research community, based on model validations, field experience, etc.), benefit/cost ratio (with respect to conventional techniques), product versatility and area of interest. The scores of each application according to these requirements are schematised in Table 1. This huge work was summarised by giving an overall scorefigureto each application, computed as a sort of weighted sum of the various criteria. As a result, one product which obtained the highest score was selected for prototyping, namely an interferometrically-derived flood. In view of the innovative character of such product, its practical implementation was performed as an assessment of the real possibilities of the interferometric technique versus more conventional, amplitudebased methodologies. The work, described in detail elsewhere [2], showed that the interferometric coherence adds a considerable amount of information to the classification of flooded/non flooded terrain. The prototype flood is shown in Figure 1.
264 GIS Technologies and their Environmental Applications 2.2 Format specifications The work also unveiled a substantial lack of standards for satellitederived GIS data. To overcome such limitations, a new kind of multilayer product standard has been defined, which is schematically depicted in Figure 2. The product format consists of a descriptive part, and the actual layer data files. The descriptive part is an ASCII file, both human- and machine-readable, arranged in a series of field names and values. This file carries information about all possible aspects related to the data understanding and ingestion into commercial software packages. It contains pointers, in URL format, to locations of both data files and documents describing their format; moreover, it carries conventional information about the geographic location of the dataset, about its size and numerical recording format, and about the data source. Any number of single layers can be included into the product, i.e. referenced in the ASCII description file. The format of the single layer data is selected so as to be as universal as possible. De facto standards have been preferred to more complete, but restricted formats. For example, DXF was chosen as the standard format for vectorfiles,and GeoTIFF for rasterfiles.the details of the format specifications are reported in a recent work [3]. 3 Conclusions An extensive study, recently performed by Planetek under ESA contract, has contributed to the definition of standards for the inclusion of satellite, remotely-sensed data into commercial GIS packages. A review of the various applications, with particular emphasis on innovative fields such as interferometry, has led to assigning a series of 'scores' to each field, as related to its suitability for inclusion into a GIS environment. Such a systematisation has helped to single out a product, namely a flood, which has been then realised as a prototype, making use of the interferometric coherence information. New standards for product formats have been proposed, and accepted by ESA. They involve both diffused and accepted numeric data formats for the single layers, and a simple, readable ASCII file, containing information of all kinds, including pointers to the data files themselves and their descriptional documents. The success of such an approach is confirmed by the recent project plans issued by ESA, such as the one indicated as "Generation of Multilayer Thematic Products for End Users" (GMTPEU), or the
GIS Technologies and their Environmental Applications 265 "Megacities" project, which clearly show an intuitive adherence to such standard formats, in their very concepts. References [1] Sylos Labini G., Samarelli S., Pappalepore M., Colonna P., Pace G., Refice A., Nico G., "GIS & Remote Sensing Final Report", PK- 9625-FR, Planetek Italia, s.r.l., 18 July 1997 [2] Nico G., Pappalepore M., Pasquariello G., Refice A., Samarelli S., "Comparison of Amplitude vs. Coherence Flood Detection Methods A GIS Application", submitted to International Journal of Remote Sensing. [3] SyloS Labini G., Pappalepore M., Samarelli S., Bequignon J., "Integrating data into Geographical Information Systems (GIS)", submitted to ESA Bulletin. GIS application Sea ice and snow Forestry Agriculture GIS products Ice edge line Ice edge movement Ice type Open water Ice motion vectors Forest/non forest Clear-cut & burnt areas Forest type Crop type Crop yield forecasting Crop change detection Table 1. Application requirements Source Single Multi-freq. Polarimetric Multifrequency Time interval Season Season Days Season Years Years Ancillary data, DEM, DEM,, Aerial Photo,, Images, aerial photos, ground truth Field boundaries; optical ; ground truth, aerial photo; ground truth Accuracy Automation degree
266 GIS Technologies and their Environmental Applications GIS application Hydrology Geology Disaster management: flooding Disaster management: oil spill Coastal areas topography land use ice disaster management GIS products Soil moisture Lineament Lithoiogicai Flooded areas Oil spill Sea bathymetry Inter-tidal DEM Coastline change detection resolution, precision DEM resolution, low precision DEM Slope Forested/Non Forested Displacement (2 ) Displacement (3 ) Differential landslide Flood Table 1 (continued). Source Muititempor al Single image Multifrequency Polarimetri c Single image Single image Several multipass interferometric pairs Interferometric pair Interferometric pair I pair - Coherence I pair I triplet I pair/ triplet I pair - Coherence Time interval months " Days' and months... Years months Days Ancillary data, DEM Land use, aerial photo, aerial photo; ground truth, land use Wind r, data, tidal currents, sea bathymetry and roughness, current drag ; DEM; None None None DEM, DEM / Accuracy (site dependent) - * - Automation degree (before and during the flood event) I ' depending on interf. Baseline and temp. Decorrelation
GIS Technologies and their Environmental Applications 267 Table 2. Potential market CIS application Sea ice and snow Forestry Agriculture Hydrology Geology Disaster management: flooding Disaster management: oil spill Coastal areas topography land use ice disaster management GIS products Ice edge line Ice edge movement ice type Open water Ice motion vectors Forest/non forest Clear-cut & burnt areas Forest type Crop type Crop yield forecasting Crop change detection Soil moisture Lineament Lithological Flooded areas Oil spill Sea bathymetry Inter-tidal DEM Coast line change detection resolution, precision DEM resolution, low precision DEM Slope Forested / Non Forested Displacement (2 ) Displacement (3 ) Differential landslide Flood Application maturity Cost/Benefit Ratio Product Versatility Area of Interest
268 GIS Technologies and their Environmental Applications Figure 1. Flooded area over Beziers delineated in darker shade. The outer black square is the scene. ASCII Human readable product main file Figure 2. Main product scheme. Standard format data files