The adjacency effect in optical remote sensing: A review on emergence, implications, and corrections for aquatic high-contrast environments

The adjacency effect (AE) in optical remote sensing emerges from atmospheric scattering of photons reflected from surrounding areas into the sensor’s instantaneous field of view (IFOV). This leads to spectral blending over heterogeneous surfaces with high contrast, expanding over horizontal distances of several kilometers and distorting the target signal. Therefore, AE can cause significant errors in quantitative retrieval of surface reflectance in high-contrast environments and further derived information, such as pixel-based chlorophyll-a concentration. This review aims to make the niche topic of AE in optical remote sensing more accessible to a broader audience. It provides non-specialists with an understanding of AE emergence, implications, and correction methods suitable for aquatic high-contrast environments. We summarized key advancements in the field, highlighting studies that introduced correction methods. We guide readers on how these studies theoretically and practically work, emphasizing their strengths and weaknesses. In the highly dynamic research field, some promising AE correction algorithms have been published recently. RAdCor and T-Mart stand out with their promising results and freely accessible nature. We applied both methods to a case study of the Osterseen Lake District south of Munich (Germany), demonstrating their application and effectiveness in correcting AE in the near-infrared (NIR) while identifying room for improvement in the visible light (VIS). These findings also reflect the broader conclusions of this review. While recent algorithms mainly concentrate on operational applicability, future research could focus on expanding AE correction to non-vegetated surfaces and regions beyond mid-latitudes.