GLOBE Transparency Secchi Disk

This is a curated dataset of NASA GLOBE observations of water transparency using a Secchi disk in fresh water, salt water, and brackish water. Depth observations are made by lowering a Secchi disk into the water until it can no longer be seen or reaches the bottom. After the disk can no longer be seen, it is lowered a further and then raised until it is visible again. Assuming that the Secchi disk did not reach the bottom, the average of the descending and ascending depths is the Secchi disk depth (denoted as transparency_disk_image_disappearance_m in the GLOBE dataset). The GLOBE Secchi Disk protocol at the time of data retrieval (September 29, 2025) also required that observers record the distance from the observer to the water surface. The distance from observer to the water surface is included in the total depth to disappearance. Most Secchi disk methodologies consider Secchi disk depth to be measured from the water surface and GLOBE participants like followed this common guidance. Inconsistencies in the dataset were found, including negative depth values. Negative values arose when observers entered a distance to the water surface that was greater than the depth of disappearance. As such, we have published this curated dataset which has been cleaned using the methods described in the README files.