Once the most known signature of the town of Koknese in Latvia was the stone castle with a large fortification system. Unfortunately, nowadays there isn’t much of the castle left, just some ruins. In early 18th century, the castle fortification system was abandoned and partially leveled by agricultural actions; the major damage was done during the First and Second World War; and finally, some of the forts were flooded down by a recently built hydro-power plant. Until 2009, the exact location of Koknese fortification system was unknown. In 2008, the researchers from the Institute for Environmental Solutions noticed surprising information in airborne remote sensing data.
1. image. Hypectral image with crop marks in a quite flat agricultural field show the missing parts of Koknese fortification system.
To identify the historical location of Koknese fortification system by airborne remote sensing.
IES planned and carried out a detailed airborne investigation of the terrain and surface of the areas adjacent to Koknese castle. The data were acquired with a twin-engine aircraft carrying a set of the most advanced sensor technologies, including LiDAR laser scanner, RGB camera and hyperspectral sensors.
LiDAR laser scanner uses light sensors to measure the distance between the sensor and the target object. From the research aircraft this includes objects such as the ground, building and vegetation. LiDAR data are very accurate, high resolution 3D data, which can be used to develop a digital terrain model (DTM) and a digital surface model (DSM). Hyperspectral images, captured in visible and near infrared light spectrum, showed us crop marks in a quite flat agricultural field.
The crop-marks can be explained by the principle of differential vegetation growth. One of the factors controlling the growth of vegetation is the condition of the soil. A buried ditch with a fill containing more organic matter than the natural earth, for example, provides much more conductive conditions and water will naturally collect there, nourishing the plants growing above. The differences in conditions will cause some plants to grow more strongly and therefore taller, and others less strongly and therefore shorter.
2.image. Digital Terrain Model (DTM) of Koknese fortification system
After data processing, we found geometric shapes in a flat field within homogeneous vegetation. It turned out that the geometric crop-marks reveal the ramparts and ditch once forming the front fortification system of Koknese fortress. State-of-the-art remote sensing data allowed us to find the information that was missing for more than three centuries. By using hyperspectral images and LiDAR data we finally obtained a full picture of the historical front fortification system of Koknese fortress. Spectral images showed us crop marks in a quite flat agricultural field.
The poster presentation made by Dr.hist. Juris Urtāns:
Project duration: 2008 – 2009
Project is financed by: Institute for Environmental Solutions
Project partner: Dr.hist. Juris Urtāns