How Altimetry Charts Work

Altimetry charts or maps show the differences in wave heights. You will have areas where the surface is higher or lower, based on upwelling or downwelling. Upwelling is where cooler nutrient rich waters are pushed up from the deep. These waters are loaded with phytoplankton and zooplankton, which are the building blocks of the food chain. Squid and all sorts of bait fish feed on this food source. In turn, bigger pelagic species are drawn to these areas of upwelling to feast on the populations of baits fish. The edges of these upwellings, as indicated on the altimetry map, are generally the best to fish. That is it, in a nut shell. Downwelling areas are the opposite. The rich nutrients are pulled down and the offshore gamefish exit the area. So, you want to fish areas with upwelling and avoid the downwellings.

How do you read the imagery showing the upwelling currents (nutrient-rich) and the downwelling currents (nutrient-poor)? You have to know what the map is telling you. In this short fishing video from In The Spread, Tom Hilton, founder of Hilton’s Realtime Navigator, a satellite mapping service for sport fishing, explains how to use altimetry when planning offshore fishing trips. You can save time and money knowing where the more productive fishing waters are, at any given time. Hilton's eiminates thee guess work. Learn how to use combined maps showing surface heights, SST, chlorophyll, currents, your trip route and more.

In Thomas Hilton's words, “altimetry data measures the upwelling cyclones and downwelling warm core eddies that are present offshore. In the northern hemisphere cyclones flow in a counter-clockwise rotation which brings nutrients up from the bottom to the surface. That plankton interacts with sunlight to start the first links of the food chain. That draws bait which attracts bigger game fish. But for every reaction there is a reaction. Warm core eddies flow downward, pulling everything with it, so there’s not much feeding going on.”

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