It has been a long-standing goal to precisely measure water-leaving radiance (L_w, or its equivalent property, remote-sensing reflectance) in the field, but reaching this goal is quite a challenge. This is because conventional approaches do not provide a direct measurement of L_w, but rather measure various related components and subsequently derive this core property from these components. Due to many uncontrollable factors in the measurement procedure and imprecise post-measurement processing routines, the resulting L_w is inherently associated with various levels of uncertainties. Here we present a methodology called the skylight-blocked approach (SBA) to measure L_w directly in the field, along with results obtained recently in the Laurentian Great Lakes. These results indicate that SBA can measure L_w in high precision. In particular, there is no limitation of water types for the deployment of SBA, and the requirement of post-measurement processing is minimum; thus high-quality L_w for a wide range of aquatic environments can be acquired.
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