Tools of the trade and hydrographic ships

A colorful lidar map of Lynnhaven Inlet, Virginia. Dark blue and black areas depict a water channel branching through the center, while lighter blues, greens, yellows, and reds depict the surrounding land. — *Lidar survey of Lynnhaven Inlet, Virginia.*

Hydrographers rely on a range of important tools to create accurate nautical charts. From laser measurement systems to tide stations, each piece of equipment fills a crucial role in gathering necessary ocean and coastal data.

One key tool hydrographers rely on is lidar, which stands for Light Detection and Ranging. While mounted to an aircraft, lidar systems send out pulses of laser light to measure coastal features and shallow water depths. Lidar uses two types of lasers: one that reflects off the water’s surface and another that can travel through the water to bounce off the seafloor. By analyzing the difference between the returns of these two lasers, hydrographers can measure water depths and shoreline elevations. This method is especially helpful in rugged or hard-to-reach areas where vessels may not be able to operate safely.

Lidar is collected over Bixby Bridge, California, with a NOAA survey aircraft (right). Lidar data shows the top-down view (top left) and profile view (bottom left) of the bridge.

Hydrographers also use topographic laser scanners, which work similarly to lidar systems but are mounted on ships. These lasers are used to measure features above the water, such as rocks, small islands, or man-made features like piers and bridges. While they can’t be used to measure underwater characteristics, topographic lasers are important for accurately mapping the coastline and identifying near-shore hazards.

A yellow water level monitoring station stands in the ocean, with a ladder to climb up to a small platform at the top.

Water level stations, such as this NOAA sentinel station off the coast of Mississippi, provide real-time water level and meteorological data.

A critical component of any nautical chart is the water depth information, which lets mariners know whether their vessel can safely travel in an area. The depth information displayed on nautical charts relies on tide and water level datums, or average water levels measured over time. Water level stations positioned throughout coastal regions collect the water level data used to create these datums. These gauges are equipped with sensors that continuously record the height of the surrounding water, providing scientists with information about depth conditions across coastal areas.

Accurate positioning information is also essential. Hydrographers rely on the Global Navigation Satellite System, or GNSS, to determine the exact location of every data point they collect. Whether marking the position of a navigation aid or mapping a shoreline feature, using GPS ensures that all of the information displayed on a nautical chart is placed precisely.

A world map showing a network of connected red points, which are distributed across continents and oceans and are connected by curved red lines. — *A precise GPS station network is used to calculate the exact location of every data point. GPS is just one of multiple global satellite networks, all of which make up the GNSS.*

A NOAA research vessel sailing on the water, illuminated by golden sunlight with snow-covered mountains in the background beneath a clear sky.

A surveying ship, the NOAA Ship Fairweather, in the Gulf of Alaska, with Mount Fairweather in the background.

Much of the data used to create nautical charts is collected from specialized hydrographic survey ships. NOAA uses four main hydrographic ships: NOAA Ship Fairweather, NOAA Ship Ferdinand R. Hassler, NOAA Ship Rainier, and NOAA Ship Thomas Jefferson. Each ship is tasked with surveying a particular coastal or offshore area to collect the information needed to support safe navigation and maritime operations.

By using advanced tools like those listed above, hydrographers collect the data necessary to produce accurate and reliable nautical charts. This ensures that mariners have all of the information they need for safe and informed navigation.