Innovative technology of maritime and terrestrial scanning for digital modelling of the relief.

Nidelea, Marinela ; Dascalescu, Ana

1. INTRODUCTION

In the present article are presented the steps covered within a research project whose objective is the achievement of innovative technologies of an integrated digital modelling, submerged and terrestrial, of the relief with coastal and riverside areas. The technology is based on the research and development of the solutions for interconnecting systems used in modern methods of investigation relief: scanning LIDAR (Light Detection and Ranging), scanning with acoustic waves of high and low frequency, mono-fascicule and rotating, positioning on the global systems with satellites, approach estimation of the movement and timing targets.

2. INTEGRATION OF SCANNING THE EARTH WITH WATER

The phase analysis, before starting the project includes the implementation of comprehensive studies and analysis on the methods of navigation, acquisition, processing and post-processing IMU/LIDAR/soundings. To develop new technologies, the project proposes a prototype of inertial platform equipped with complex systems of underwater and over terrestrial scanning which can be mounted on a boat and also on a land motor vehicle, and validating the performances of the new mixed soil water technologies--as an alternative to unique functional airy, land or sea solutions. The benchmark of the first stage of the project is studying the possibility of integrating the earth scanning systems with the water systems.

The scientific research aimed primarily to deepen the knowledge in the methods of acquisition and data processing specific for scanning the relief.

The complexity of the new technology to be developed results from the need of interconnecting the advanced equipment, with dedicated operating software, in synchronization conditions in time and space. The technology aims that the distances measured by ultrasounds or laser to provide the position of some points on the Earth surface, with high density and precision, whether the emission source is stationary or moving and that attitude sensors shape of a boat movement (rolling, pitching, swell) or the movement of a vehicle on rough land. Based on the points cloud such acquired and corrected, digital models that can describe the relief more objectively can be developed (Milman, 2007).

In order to establish the criteria by which are guided the next phases of the project, we studied the traditional lifting methods and scanning methods both land and hydrographical, the representative equipments, the principles of operation, the errors that may affect the measurements and the possibilities of integration.

3. THE 3D LAND SCANNING

The relatively new technology of terrestrial laser scanning has a great interest among engineers, architects and archaeologists involved in the data collection for inventory and protection of the monuments, or using the monitoring applications and structural analysis.

The terrestrial scanning systems have evolved with the technologies that are behind the total electronic stations [with predilection the SST (System Scan earth) flight-time]. Also the rapidly development of the technical computing (memory, computing power and processing) has also contributed decisively to the development of this technology. This rapid evolution of SST and the advances made in land technology based on electromagnetic waves and the calculation technique, allow us to extrapolate and predict an increasingly availability to these laser scanning systems (Navulur, 2007). The determination of areas with more complex details is more easily achieved by laser scanning, than the case of stereo photogrammetric, especially in the case of complex objects and/or with sharp edges, which recommends it not as an opponent but as a reliable partner of the photogrammetric land from short distance.

4. SCANNING SYSTEMS AND PRINCIPLES OF OPERATION

The building companies of the LASER scanning systems often offer an adjusted version (more advertising) in their presentation. A raid on their Web site often proves to be a hazardous journey if the technology behind these systems it is not known. The criteria used in making the classification are: work field from the point of view of the measured distance, the precision of the distance measurement, measuring principle, the diversion of LASER beam, the angular field of the LASER scanning, etc. Within the project is presented a classification after the principle measurement considering that this criterion is exhaustive and covers very well the other criteria.

The principle of operation is similar to the total electronic stations that can measure in the "no light" mode.

The differences between ST (total station) and SST terrestrial (scan systems) lies in the large number of measured distance (and based on the measured angles will result the positions of the scanned points) per unit time (advantage) but also by low redundancy (disadvantage) among the measured distances "filtering" non-filtered and the distances contaminated by the multipath effect. The harmful results of this effect are offset by attaching an auxiliary device (typically a webcam), by the measuring method of or even by processing and post-processing of the points cloud.

From the combination between the scanner, program and the webcam, result the following advantages:

* the automatic generation of the digital models of the land;

* Playing a real 3D model;

* Identify with precision the details;

* The automatic generation of the 3D ortophotogram.

5. THE DATA PROCESSING

The data processing must be made under strict criteria of quality control.

The hydrographical data are either collected by the automated systems or are converted into a format that can be further processed automatically. The final data processing and printing the results is done with the aid of computer systems from the board of the ships or from the office (Millet & Evans, 2002).

The data collected are processed and subsequently, any failures or data whose validity is questioned are collected again. The most water systems are able to conduct operations "carried out the ground" when collected data are processed, printed and analyzed in the collection area, on the field.

6. INTEGRATION POSSIBILITIES OF THE LAND AND WATER SCANNING SYSTEMS

The starting element in searching the integration solution is the experience in installation, calibration and use of water multi fascicule systems.

An example of integrating a terrestrial scanning system, a system which is used in investigating the underwater pipeline from the oil field of the continental shelf of the Black Sea, contains the most important components on hydrographical scanning: RTK positioning system, motion sensor, gyrocompass, well for measuring the speed of sound, mono fascicule and multi fascicule well, the unit for synchronization in time, the onboard computers and software for navigation and the hydrographical data acquisition (Plopeanu, 2008).

Through integration with an inertial navigation system, the 3D laser stationary station can become a mobile system similar to the laser scan solutions of the plane, with the difference that the laser beam is focused on the lateral direction for the submission of a land vehicle.

The final step in integration represents the mounting of the scanning station to the board the craft that makes the measurements and achieving the data that are synchronized in time and space (4D), both for the land covered by water and the land above the water from the coastal or river areas (DYNASCAN Project, 2008).

To develop new technologies the project includes the realization of a prototype of inertial platform equipped with complex underwater and over terrestrial scanning systems that can be placed both on ship and on ground, as well as the validation of new mixed water ground technologies as an alternative to solutions terrestrial or marine.

This work is something new at national level. During the development of the project and with the end of the rehabilitation of the Sulina canal images of the same type were processed and grouped in data sets as can be seen from the following image.

[FIGURE 1 OMITTED]

Geometric processing of images in the processes that occur at the level of digital photometric systems is done by the soft of digital photometric application to bring in coincidence the stereo image plan with the plan on the field.

The disadvantage of the proposed method is that if the distribution of permanent GPS stations is insufficient, the acquisition of data with enough accuracy is still expensive.

Of course we must emphasize that during the process of data acquisition and processing, cumulative errors may appear and in the end these must not surpass the current standards.

7. CONCLUSIONS AND FINDINGS

As a result of this research we can state that by using the proposed platform the subjectivity of classical methods is almost entirely eliminated. This will allow a more accurate representation of the land in the post-processing step.

Further research should validate if the proposed technology and methodology lead to results at least as accurate as the classical method but in a shortest time and with fewer resources.

The method is fast on small areas and can be used for natural disasters situations.

In conclusion we must remark that the images obtained suffer a complex technological process so that we can obtain from their content the geometric position of topographic objects in the field with a high degree of accuracy.

8. REFERENCES

Milman, A. (2007). Mathematical Principles of Remote Sensing, Kindle, ISBN 1575041359, USA

Navulur, K. (2007). Multispectral Image Analysis Using the Object--Orinted Paradigm, CRC Press, ISBN 1-4200-4306-4, New York

Millet, N.; Evans, S. (2002). Working with the Geodatabase, Environmental, Systems Research Institute, February 2002, pg. 6-8, ISSN 0098-3004

Plopeanu, M. (2008). Fenomenul de predictie in masuratorile geodezice. Analele universitatii din Oradea, Vol.14, may 2008, pg.30-35, ISSN 1454--4067

*** (2008) DYNASCAN Project--Innovative Technology of the river-maritime and land scanning for digital modelling of the land, Insert Hydrographics, pg. 95-110, research report submitted to AMCSIT, under no. 5073/28.11.2008