Selected problems with determination of resolving power of sensors used during Open Skies missions

Precyzyjne wyznaczanie terenowej zdolności rozdzielczej sensorów jest kluczowym problemem przy pozyskiwaniu zobrazowań z pułapu lotniczego, zwłaszcza w ramach traktatu Open Skies. Ustalono w nim minimalną, dopuszczalną, terenową zdolność rozdzielczą dla poszczególnych rodzajów sensorów. Ponieważ rozdzielczość terenowa większości rodzajów sensorów jest uzależniona od ich wysokości nad odwzorowywanym terenem, konieczne jest wyznaczenie minimalnej wysokości lotu obserwacyjnego, na której dozwolona rozdzielczość terenowa nie zostanie przekroczona. W tym celu wykonuje się przeloty i pozyskuje zobrazowania nad specjalnie skonstruowanymi celami kalibracyjnymi. Na pozyskanych zobrazowaniach mogą występować pewne błędy, artefakty, mające wpływ na poprawność wyznaczania zdolności rozdzielczej. W przypadku badań w zakresie widzialnym błędy spowodowane są przeważnie pracą sensora oraz sposobem rejestracji danych. W przypadku sensorów termalnych, dodatkowym elementem mogącym wprowadzać błędy są same cele kalibracyjne. W Zakładzie Teledetekcji i Fotogrametrii WAT prowadzone są obecnie prace nad stworzeniem nowych celów kalibracyjnych, których konstrukcja będzie minimalizowała te błędy.The precise determination of resolving power of sensors is a key problem especially when establishing which sensors can be used for Open Skies missions. The Treaty on Open Skies dictates the lowest acceptable resolving power of sensors which can be used during observation flights. Because the resolving power of most sensors differs with the height of the sensor above the terrain, it is essential to determine the minimal flying altitude, at which the permitted spatial resolution will not be exceeded. A series of test flights above especially constructed calibration targets is conducted in order to acquire imagery of these tests at different altitudes. The spatial resolution of these images is determined by evaluating the visibility of each of the components of these calibration targets. In theory, such a methodology would allow for the precise calculation of the resolving power. In reality, however, the acquired images can be burdened with a number of artifacts, or deformities, which can have a negative effect on accuracy of our calculations. When acquiring imagery in the visible range, these errors are usually caused by the detector itself or by the method by which the data is registered. However, imagery in the thermal range can additionally contain errors caused by the design of the calibration targets used. In recent years, at the Department of Remote Sensing and Photogrammetry at the Military University of Technology in Warsaw, we have designed and constructed a number of calibration targets used during Open Skies missions. One such target had been recently laid out during a Ukrainian observation flight over Polish territories. The aim of the experiment was to establish the resolving power of a new Ukrainian film. A series of images had been acquired by means of the AFA-41/7.5 analogue frame camera from a height of 1100 m. This height is the theoretical Hmin for this film, meaning the spatial resolution of imagery acquired from this altitude, will be close to 30 cm. Based on imagery acquired during this flight, it had been established that the spatial resolution of the resultant imagery is much worse than 30 cm, which means that the chosen Hmin value had been too high. We are currently in the process of constructing a new set of calibration targets, whose design will minimize the aforementioned errors. Additionally, the targets have been designed in such a way, that they will be used for determining the spatial resolution of both thermal and optical sensors. The effectiveness of these new targets will be tested shortly