*Recent Advances in Oil-Spill Monitoring Using Drone-Based Radar Remote Sensing DOI: http://dx.doi.org/10.5772/intechopen.106942*

than unity, the decision indicates the oil's existence. Otherwise, the decision indicates that the seawater surface is clean. We note that the probability of obtaining a measured reflectivity value given that the oil or water exists is evaluated using the corresponding probability density function (pdf). For this, we propose several algorithms for different detectors:


**Figure 4** shows the performance of dual-frequency detectors. For clarity, we also show the performance of the detectors running each of the two scanning frequencies separately. Evidently, the dual-frequency detectors outperform the single-frequency

#### **Figure 4.**

*Comparison between the probability of detection and the oil thickness (in mm) for different detector algorithms: Single-frequency detectors at 4 GHz, 8 GHz, and 12 GHz, and dual-frequency detectors using combinations of these frequencies.*

detectors. At thickness values where the accuracy of a single-frequency detector is low, the dual-frequency detector gives more weight to the decision of the pair detector. For instance, a 12 GHz detector performs poorly for d = 7.2 mm because it has the same reflectivity value as the water (refer to **Figure 2**). However, the (4 GHz, 12GHz) detector optimally tracks the performance of a 4 GHz detector.

Although dual-frequency detectors are better than single-frequency detectors, there are still some thickness ranges where the probability of detection is affected by the ambiguity points. To boost the performance of the detection, we increase the number of frequencies K and observations M. Results in **Figure 5** show that a higher probability of detection is further obtained over the full range of thicknesses. Using three frequencies (4 GHz, 8 GHz, 12 GHz) and two scans (M = 2) of the target scene, the detection accuracy is above 90% for all thickness values above 3 mm. Additional scans would further be required to improve the probability of detection of thin oil slicks. Fortunately, performance requirements are less strict for small thickness values. By comparing the performance of the tri-frequency detector with single observation to the dual-frequency detectors with double observations, we notice that the first detector is better since it provides a very high percentage of correctness at the large thickness values (i.e., cases where oil detection is crucial) and very good behavior at small thickness values, which are more challenging for oil detection but less severe in false alarm scenarios. Additionally, the performance of the detectors is studied under a blind detection scenario in which the scanning of the scene is done without any knowledge about the exact or the estimated thicknesses of spilled oil. This type of detection is based on the joint-pdf that takes into consideration all the possible thicknesses with their probabilities in order to weigh the final decision. The distribution of oil thickness is assumed to be uniform over the range (0–10 mm). Results show the same behavior as detailed in [72]. The detector can provide correct decisions in different thickness ranges at different frequencies. The probability of error can be decreased by using dual- and tri-frequency detectors. Additional error can be

#### **Figure 5.**

*Comparison between the probability of detection and the oil thickness (in mm) for different detector algorithms: Dual-frequency detectors and multi-frequency detectors, using single (M = 1) and double observations (M = 2).*

*Recent Advances in Oil-Spill Monitoring Using Drone-Based Radar Remote Sensing DOI: http://dx.doi.org/10.5772/intechopen.106942*

compensated by using more scans. However, in the range where the oil thickness is small (< 2 mm), the probability of detection does not exceed 65% indicating low certainty.

Previous results are obtained under the assumption that the surface is smooth due to very low wind speeds and calm ocean conditions. For higher wind speeds and rmsheight of the seawater, the surface roughness increases. We present the performance of the detectors for different roughness scenarios in detail in [69]. Results show that the performance overall is reduced.
