Late March

A flyover early in the month proved fruitful, since it was done after plowing. Since then, it has rained a great deal. As soon as the atmospheric conditions permit, a new flyover is planned.

Fortunately, the weather forecast calls for clear skies on the 26th or 27th. Having contacted our usual pilot, we reserve a plane for those dates at the flying club, where we are members, and plan to take off around 7 a.m.

Preparing for the mission

To prepare for this new mission, long hours are spent reviewing the sites that were discovered in previous years and closely examining the photographs that have been taken, to determine if certain sites should be the object of new flyovers in order to complete the data that we already have.

If this is the case, we locate them on the IGN map that we will take on board with us, because it is particularly suited to our needs. The scale of 1/100,000 let us cover a fairly large surface, and makes it easy to recognize wooded areas, as well as the shape of villages, waterways, and road and rail networks.

Certain aerial prospectors use the Michelin maps. The cross-hatching on the map indicates zones that need to be prospected more closely, since up to the present they have yielded nothing.

The day before takeoff

We have to contact the farmers that we know and make a trip out into the fields. This will help us better understand how the agricultural work is advancing, depending on the type of terrain, and to prioritize our flyovers.

The day

It's raining cats and dogs on the morning of the 26th. The flight must be delayed, especially since the weather forecast promises a sunny day tomorrow.

The next day

At the same time on the 27th, there is a thick fog… and that means good weather. We have to wait until it breaks up a bit, so we drop in at the weather station.
On the station screens, we can see that it is much clearer in the east. We decide to quickly take off and fly in this direction, before the fog has entirely disappeared.

Equipment check

When we arrive at the aerodrome, the pilot performs a regulation check-up. Armed with his flight log and aeronautic map, the pilot checks the oil and gas levels, and makes sure that the plane is in good working order.

For our part, we check our camera equipment and film supply, and make sure we have our 1:100,000 scale maps, on which we have marked our objectives. We also take along a set of 1:25,000 scale archaeological maps, which we rarely consult while in the air, but which have come in handy on certain occasions.

It is also useful to bring along a tape recorder to record our observations, and a GPS system that will supply us with the geographic coordinates of the sites we photograph. Most flying club planes are now equipped with this system.

Thérouanne en 1539, peu avant sa destruction par Charles Quint. La consultation de documents d'archives est utile à la préparation de la mission. Photo : Archives départementales du Pas-de-Calais.

La veille du décollage

Il faut prendre contact avec les cultivateurs que nous connaissons et faire une grande excursion dans la plaine. Cela permet de mieux connaître l'état des travaux agricoles, selon les types de terrain, et ainsi de savoir ce qu'il faudra survoler en priorité.

Jour J
Le 26 matin, il pleut à verse. Il faut remettre le vol d'autant plus que la météo promet une journée ensoleillée pour le lendemain.

J +1
Le 27 à la même heure, il y a une forte brume… prometteuse de beau temps. Il faut attendre qu'elle se dissipe un peu, nous passons à la station météo.
Sur leurs écrans, nous voyons apparaître une amélioration très nette vers l'Est. Il faut partir assez vite dans cette direction, avant même que la brume ne soit entièrement dissipée.

" Check-up " : vérification du matériel
A notre arrivée à l'aérodrome, un " check-up " réglementaire est fait par le pilote qui, muni de son carnet de bord et de la carte aéronautique, vérifie le bon fonctionnement de l'appareil, les niveaux d'huile et le plein de carburant…

De notre côté, nous vérifions l'état de nos appareils photographiques, la réserve suffisante de pellicules et de cartes au 1/100.000e où nous venons de pointer nos objectifs. Nous prenons également en réserve des cartes archéologiques complètes au 1/25.000e, rarement consultées en vol, mais qui, dans certains cas particuliers, se révèlent intéressantes.

Il est aussi utile d'emporter un magnétophone pour enregistrer nos observations et surtout un GPS qui fournira les coordonnées géographiques des sites photographiés. Toutefois, la plupart des avions d'aéro-clubs en sont maintenant équipés.

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Photo aérienne de la ville de Thérouanne. On voit réapparaître de façon
spectaculaire l'ancien rempart qui entourait la ville.

Dernier " check up " de l'appareil avant de partir...