Photogrammetry for the Preparation of Archaeological Excavation (Part I)

A 3D Restitution According to Modern and Archive Images of Beaufort Castle Landscape (Lebanon)


1930-1936: Archive images of the French Air Force of the Levant (aerial large format images)


2003: Modern digital images (aerial and terrestrial small format images)

1. INTRODUCTION

The Fort of Beaufort is a medieval castle constructed by the crusaders, the Ayyubids and the Mamluks. The castle is located in the southern part of Lebanon, a few kilometers far of the Israeli border. It is one of the emblematic monuments attesting the successive occupations of the site. After the Israeli withdrawal of southern Lebanon, the Lebanese government commissions a multidisciplinary team to establish a preliminary study for the restoration of the castle. This team is composed of many specialists and is headed by Jean Yasmine, a consultant at the Directorate General of Antiquities (DGA). This team is responsible of the establishment of tender documents for contractors. There are many works on this important monument (dimensions of the castle: 75m x 150m; height. 30m; dimensions of the surroundings: 200m x 500m). There is archaeological excavation. There is consolidation and restoration of structures and surfaces. There are also cultural and touristic equipment in the scope of works. The present paper deals with the preparation of archaeological excavation and restoration tasks, by showing the destroyed historical structures.


Figure 1. Recent aerial view of the Beaufort castle (Nikon F3, 2003)

2. HISTORIC OVERVIEW OF THE CASTLE

There is no text related to the castle before the arrival of the crusaders. This rock crest overlooks the passage towards the Syrian hinterland. It is difficult to imagine that there was not a fortified point controlling this passage before the arrival of the crusaders.
The texts say that Beaufort was deserted and taken by the crusaders in 1139. A few years later, Beaufort was ruled by the Lord of Saïda (Sagette). In the year 1179, a battle between Baudoin IV and Saladin took place while Renaud de Sagette was the master of the castle. Saladin took Beaufort in 1190, after a one year siege. A few years later, before the arrival of the Mamluks, Al Salih Ismaïl made a deal with the crusaders and gave them the castle back in 1240. In 1260, Julien de Sagette sold the castle of Beaufort to the Order of the Temple. This order kept the castle until 1268. On that date, the Mamluk Sultan Baibars besieged Beaufort and took it. Restoration works and new constructions are attested in Arab texts.

The 14th, 15th and 16th centuries were calm.

In the 17th century, during the reign of Fakhreddine, a prince of Lebanon, the castle became part of his fortified net. After the defeat of Fakhreddine, the ottomans destroyed the upper structures of the castle. Between 1616 and 1769, the area was ruled by feudal families. In 1782 `Al jazzar governor of cAkka (Saint Jean d'Acre) besieged the castle, took it and destroyed its fortifications.

In 1837, an important earthquake destroyed many parts of the castle. After this date, it became a quarry for the neighborhood and a sheep-fold.

During the same period, in the late 19th century, the Orientalists came and described the castle (successively Rey, Guérin, Conder & Kitchener). The castle was quiet in that period.

After 1920, there was the French mandate on Syria and Lebanon. The French emphasized on the crusader period sites. The authorities began to consolidate and to restore these castles. A first survey and documentation of the site was done in 1936 by the architect Pierre Coupel showing the means of access to upper courtyard of the castle (figure 2). After the independence of Lebanon in 1943, extensive works began.


Figure 2. Map of Pierre Coupel (Architect) drawn up during the Deschamps survey (1936)

Lately, the castle became again a strategic stake in the war of Lebanon. Between 1976 and 1982 it was occupied by the Palestinians who attacked from this fortified point the North of Israel. Between 1976 and 1980, dozens of raids were made on the castle. On June 6th, 1982, it was heavily shelled before it fell in the hands of Israelis on June 8 of that year. The destructions we see nowadays date from that period. The Israeli army stayed there and fortified the surroundings with bunkers and reinforced concrete blocks.
Finally, in the year 2000, the Israeli army withdrew from the castle after the attacks of the Lebanese resistance.

3. THE THREE-DIMENSIONAL RESTITUTION AND THE AIM OF THE RESEARCH

The problem raised for the restitution of the historic surroundings is the preservation of the archaeological remains while excavating the spoil heap dating of the war. Many of these archaeological remains can be seen on historical documentation.

3.1 The historical documentation

Many series of historical photos of the castle exist.

a- Serie 1: These are the photos of the publication of Paul Deschamps (Les châteaux croisés en terre sainte, t. II, La défense du royaume de Jérusalem, Ed. Geutner, Paris, 1939). A little part of these photos were taken by the French air force of the Levant between the years 1930-36. These photos are only available in the publication. The original negatives were never found. The use of this documentation is difficult within the scope of this project; they can only be indicative photos.

b- Serie 2: These are photos still existing in the Institut Français du Proche-Orient (IFPO) archives (figure 3). All these photos were taken by the French air force of the Levant between the years 1930 and 1936. We were able to get duplicates (contact prints) of negatives at a size of 13cm x 18cm, scanned on a desktop scanner.


Figure 3. Example of archive photo of 1936 (IFPO), showing in the foreground the archeological hidden remains

c- Serie 3: These are photos existing in the archives of the DGA. All these photos were taken by the French air force of the Levant between the years 1931 and 1936. They are vertical views (figure 4). Only contact prints at a size of 13cm x 18cm are available; the original negatives were not found. Those contact prints were scanned.


Figure 4. Example of archive photo of 1935 (DGA, area of Beaufort’s castle), showing the castle (in the middle) and the landscape (focal length 26cm, flying height 1300m above ground, 2000m above sea level)

3.2 The modern documentation

After the end of the war, access to the castle became secure. There was a need to manage to realize a complete documentation of the unreachable parts of the castle (basically the eastern elevation over the valley). That’s why a helicopter flight was scheduled in 2003. Aerial oblique views were taken (figure 1) in that flight. They were composed of digital images (Nikon Coolpix 5000, 2560x1920 pixels) and film-based small format color slides (Nikon F3, Nikkor lenses, 55 mm, scanned at a resolution of 3000x2000 pixels). Last but not least, a complete documentation requested terrestrial views of the castle; digital images and again film-based small format color slides were taken (figure 5). Thanks to this exhaustive documentation, three-dimensional restitution was possible. All the modern documentation was produced in one day.


Figure 5. Recent terrestrial digital image (modern documentation, Nikon Coolpix 5000, 2003)

3.3 The topographic survey

On that same day, while photos were being taken, a team of geodetic surveyors installed reference points on the ground and elevations of the castle. These points (figure 6) were easy to identify on the photos. A total-station was used by the surveyors to measure the reference points. This generated threedimensional coordinates for these points.






Figure 6. Examples of targets used for the control points

3.4 The AutoCAD documentation

The first topographic surveys conducted during the preliminary study were not very accurate due to the difficulties encountered in trying to access some of the areas of the castle. These first surveys were performed using GPS and tacheometric techniques. The AutoCAD maps (figures 7 and 8) used to establish the tender documents for the restoration of the castle were based on these surveys. The inaccuracies of these surveys did not represent a major problem for the restoration of the visible areas of the castle. However, these inaccuracies prevented us from computing the exact position of the archaeological hidden remains. We plan to generate a new AutoCAD documentation showing the surroundings of the castle and the archaeological hidden remains that should be dug out (§5).


Figure 7. Example of 2D AutoCAD map from the tacheometric survey of 2002 (level 4 of the castle)


Figure 8. Example of 2D AutoCAD section

Photogrammetric Data Processing will have to wait in the next post....

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