Corrosion has a large negative effect on the service life of metallic substrates, such as cars, bikes and boats. To reduce the corrosion rate, the bare metal can be isolated from the corrosive environment by applying an organic coating (paint). As metals corrode, organic coatings degrade. Temperature, wet-dry cycles and UV-light all have an effect on the lifetime of an organic coating. Maintenance of these systems is therefore of vital importance to guarantee the coating still provides sufficient protection against corrosion. While in theory Electrochemical Impedance Spectroscopy (EIS) can give valuable insight in the condition of a applied in situ coating system, this method is seldom used outside laboratory mainly due to the complexity of the setup. In this master thesis, a new EIS setup and interpretation method are introduced to reduce the complexity of EIS method for in situ measurements. To validate this new method, laboratory coupons with different aircraft coatings were degraded in salt-spray and UV-condensation cabinets. These coupons were frequently measured during the degradation process with a normal EIS setup and the new handheld setup. With these measurements, the interpretation methods and setups were compared. The same procedure was executed on a location outside the laboratory, the Oosterscheldekering, the measurements were compared with result values of measurements performed five years ago. The result values of the measured laboratory coupons showed comparable degradation trend with both measurement setups. The same was observed with the measurements on the Oosterscheldekering. The interpretation method exhibited an easy way to present the coating condition, although is not able to show complex physical processes occurring when the corrosion process starts. Overall, it can be concluded that the handheld sensor setup with the simplified interpretation method is very good technique for in situ organic coating assessment on metal substrates. With the condition that the measurements are performed by someone who is experienced in the use of Electrochemical Impedance Spectroscopy and who understands the discussed shortcomings of the system.