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2.0 DESCRIPTION OF THE PROPOSED ACTION AND THE ALTERNATIVES

The National Environmental Policy Act (NEPA) requires federal agencies to analyze a proper range of 

reasonable alternatives to satisfy the Purpose and Need (see Section 1.3). To be considered a reasonable 

alternative, the National Ocean Service (NOS) determined that a proposed alternative must:

• Be technically feasible;

• Not violate any federal statute or regulation;

• Be consistent with reasonably foreseeable funding levels; and

• Meet national, regional, and local data needs.

Based on these criteria, NOS identified two action alternatives that meet the stated purpose of the 

proposed federal action and thus have been analyzed in detail. These alternatives are presented in 

Sections 2.5.2 and 2.5.3.

NOS also analyzed a “No Action” alternative that allows the reader to compare the potential impacts of 

either action alternative with the effects that would occur if NOS continued coastal and marine data 

collection at current levels using current technology and methods (i.e., the status quo). The No Action 

alternative is presented in Section 2.5.1.

2.1 ALTERNATIVES CONSIDERED BUT ELIMINATED FROM FURTHER ANALYSIS

Early in the NEPA planning process, NOS considered a range of alternatives to the Proposed Action before 

arriving at the three alternatives presented in this Programmatic Environmental Impact Statement (PEIS). 

The alternatives presented below were eliminated from further analysis because they did not meet one 

or more of the screening criteria listed above.

2.1.1 Protected Species Avoidance

NOS considered whether to discontinue hydroacoustic surveying, mapping, charting, or related data 

gathering in waters with known populations of federally protected species such as marine mammals. 

Protected species avoidance would include complete avoidance of all Biologically Important Areas (BIAs) 

such as preferred breeding, feeding, and nursery grounds or migratory routes. BIAs are discussed in 

Section 3.5.1.1.2 of the PEIS. BIAs indicate locations where particular species engage in biologically 

important behaviors either year-round or seasonally. BIAs were created to help the National Oceanic and 

Atmospheric Administration (NOAA), other federal agencies, and the public in the analyses and planning 

used to characterize and minimize the impacts of anthropogenic activities on cetaceans and to achieve 

conservation and protection goals. BIAs occur in every region throughout the NOS action area, but they 

do not present the totality of important habitat throughout the marine mammals’ full range. Recognition 

of an area as biologically important for some species activity does not cause the area to rise to the 

designation of critical habitat under the Endangered Species Act (ESA). The stated intention is for the BIAs 

to serve as a resource management tool and for their currently identified boundaries to be considered 

dynamic and subject to change based on any new information.

Time-area restrictions for BIAs would significantly impact the ability to collect data during suitable 

conditions for using acoustic sources, result in lost survey time, and affect the crew’s ability to work safely.

For example, BIAs in Alaska are located throughout Alaska as shown below (Figure 2.1-1); some are 

seasonal and other are year-round. Prohibiting data collection in these areas would not allow NOS to meet 

the purpose and need for the Proposed Action.
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Figure 2.1-1. Biologically Important Areas in Alaska

NOS also considered the necessity and practicality of additional mitigation measures for BIAs. In 

coordination with the National Marine Fisheries Service (NMFS) and U.S. Fish and Wildlife Service 

(USFWS), NOS has developed mitigation measures that include maintaining safe distances from marine 

mammals achieved by decreasing vessel speeds, vessel maneuvering, and observing time-area restrictions 

in specific protected species habitats (e.g., North Atlantic right whale). NOS already uses the lowest power 

appropriate to perform surveys, and employs mitigation measures including protected species observers 

(PSOs) to ensure that marine mammals are not within the vicinity of the vessel when active acoustics are 

being used. During nighttime operations, NOS uses the appropriate lighting to comply with navigation 

rules and best safety practices. All project areas would be continually monitored for protected species by 

posted crewmembers during vessel operations.

Any further mitigation, including entirely prohibiting mapping and surveying data collection or time-area 

restriction within the BIAs as discussed above, is unwarranted and impracticable due to safety concerns.

For example, such restrictions could force NOS crews to operate at times and locations where sea 

conditions prevent safe vessel operation. Additionally, time-area restrictions for BIAs affect data 

collection and continuity and result in lost survey time NOS believes that the implementation of mitigation 

measures to further reduce the minor and temporary expected impacts will provide substantial protection 
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for marine mammals during NOS surveying and mapping activities and complete avoidance of protected 

species and BIAs is unnecessary.

This alternative would prevent NOS from providing the coastal and marine data necessary for safe 

navigation, economic security, and environmental sustainability in large parts of U.S. waters. Therefore, 

NOS rejected this alternative because it did not allow national, regional, and local data needs to be met.

2.1.2 Use of Lidar Exclusively

Bathymetric Light Detection and Ranging (lidar) technology measures depths of nearshore waters using 

laser pulses emitted from a scanner on board a low-altitude airplane typically flying at speeds of 140 to 

175 knots. The aircraft typically flies at altitudes of 300 to 365 meters (m) (1,000 to 1,200 feet [ft]) for up 

to five hours per flight. Lidar systems used for bathymetry emit visible green laser pulses to measure the 

timed sea floor bottom return, and near-infrared laser pulses measure the sea surface return. Depth is 

determined by the time of the return back to the lidar sensor from the energy reflected off the sea floor.

Lidar technology can efficiently survey large areas, identify features in a short period of time, and safely 

survey nearshore areas that are hazardous to mariners. However, lidar has distinct limitations in deeper 

water and under challenging environmental conditions. Variables such as water clarity (turbidity), sea 

state, and sea surface limit the effectiveness of bathymetric lidar. In particular, lidar does not produce 

good results when used in turbid waters. Under non-ideal conditions, lidar systems often fail to identify 

small, potentially hazardous objects on the sea floor. Even in the best conditions, reliable laser “returns” 

from the sea floor diminish in waters deeper than 20 to 30 m (65-98 ft).

NOS rejected this alternative because it does not meet national, regional, and local data needs, and thus 

fails to meet the stated purpose and need. Relying on lidar exclusively would not meet the accuracy 

standards needed for reliable charts, maps, and other products.

NOS may use lidar on individual projects, where appropriate, such as for shoreline verification. However, 

these lidar surveys are not within the scope of this document.

2.1.3 Use of Satellite-Derived Bathymetry Exclusively

Satellite-derived bathymetry (SDB) refers to data from optical satellite imagery. SDB begins with using 

multi-spectral satellite imagery, such as Landsat, Sentinel-2 and WorldView2, and calculating a ratio 

between green and blue color bands. Because of the optical nature of green light to attenuate faster in 

the water column than blue light, the blue/green band ratio can help to infer relative depths of the water. 

Using control points, SDB results can be referenced to chart datum. Unlike “active” depth measurement 

techniques that measure depths directly using “time-of-flight”, such as echo sounders or lidar, where 

controlled signals are transmitted and the return time is measured and used to calculate the water depth, 

SDB is a “passive” technology and is simply measuring the reflected sunlight intensity that is used to infer 

the water depth.

Similar to optical systems like lidar, environmental conditions (e.g., water turbidity, cloud cover, and sun 

glint) can degrade accuracy, which prevents SDB from being used exclusively as a replacement for 

hydroacoustic methods. Therefore, NOS rejected this alternative because it does not meet national, 

regional, and local data needs, and thus fails to meet the purpose and need for this Proposed Action.
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NOS may use SDB as a reconnaissance tool on a case-by-case basis for investigating coastal areas before 

performing a high-resolution hydrographic survey with traditional methods. However, this use of SDB is 

not within the scope of this document.

2.2 COMPONENTS OF THE ALTERNATIVES: PROJECTS AND ACTIVITIES

NOS collects data in United States (U.S.) waters each year by undertaking a number of discrete surveying 

and mapping projects, which comprise the alternatives evaluated in this Final PEIS. Projects include, but 

are not limited to, hydrographic surveys, marine debris surveys, tide gauge installation, and benthic 

habitat characteristic surveys. A project would typically consist of several individual components, which 

are referred to in this document as “activities.” Figure 2.2-1 depicts many of the activities which are 

combined by NOS program offices to compose a given project. 

Figure 2.2-1. Common Activities Used in NOS Projects

The nature and scope of projects can vary based on the combination of activities. For example, a habitat 

characteristic survey could consist of crewed vessel use, diving using Self-contained Underwater Breathing 

Apparatus (SCUBA), Remotely Operated Vehicle (ROV) use, multibeam echo sounder use, and bottom 

sampling. The individual activities are described in Section 2.4 below.

Another example is an NOS Office of Coast Survey (Coast Survey) hydrographic survey project performed 

to update nautical charts for waters off the coast of California. Once planners identify the area that 

requires updating, a vessel such as the NOAA Ship Rainier would be tasked with the project, sailing from 

its home port in Newport, Oregon to the project area. Once there, the ship’s crew would map the sea

floor of the project area with multibeam echo sounders while also collecting water column data, and 

determine seafloor type by collecting and examining sediment. Once all of the required data are collected, 

Rainier might return to port, or head directly to its next project. In this example, the survey project 

includes the activities of crewed vessel operation (Section 2.4.1), echo sounder use (Section 2.4.4), 
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conductivity, temperature, and depth (CTD) instrument use (Section 2.4.7), and collection of bottom grab 

samples (Section 2.4.9).

Some NOS projects involve or include terrestrial work. For example, a field crew from the NOS Center for 

Operational Oceanographic Products and Services (CO-OPS) may take a small boat to a coastal area where 

planners have determined that more precise data on local tides and currents are needed. Upon arrival, 

the crew would determine where a new tide gauge station should be located (such as on an existing pier) 

and what type of gauge is needed. A SCUBA diver would enter the water to install the underwater 

elements of the pressure sensor for the tide gauge. The crew would install other components, and then 

test the gauge to ensure that it is operating correctly before leaving the site. The activities for this project 

therefore include crewed vessel operation (Section 2.4.1), tide gauge installation (Section 2.4.12), and 

SCUBA operations (Section 2.4.11). 

The responsible NOS program office(s) sets the goals and purpose of a given project and determines the 

specific equipment and protocols to be used. For instance, Coast Survey conducts hydrographic surveys 

using a combination of high-frequency side scan sonar and single beam and multibeam echo sounders. 

During a Coast Survey hydrographic survey, a vessel equipped with one or more echo sounders "mows 

the lawn" at a slow speed to ensonify (or visualize) the sea floor bottom and ensure full coverage of the 

sea floor within the project area. Coast Survey conducts surveys primarily in shallower waters critical for 

safe navigation, where depths are low and the need for precision is high. As a result, Coast Survey uses 

primarily high-frequency (40 to 1,000 kilohertz [kHz]) echo sounders during survey operations, but may 

use low- to mid- frequency echo sounders in deeper areas where high resolution charting is not necessary. 

When large ships are surveying for an NOS mapping project, they often operate the echo sounders 24 

hours per day. Surveys using small vessels are typically shorter in duration (8 to 12 hours). These survey 

protocols are determined by project needs. Other program offices similarly select equipment and 

protocols commensurate with the goals of a given project.

In many cases, a single NOS program office is responsible for a project; in other cases, multiple NOS offices 

may cooperate, or an office may work with colleagues from other parts of NOAA or other federal agencies. 

For example, Coast Survey routinely collaborates with the Office of Marine and Aviation Operations 

(OMAO), a NOAA component separate from NOS, to have vessels such as NOAA Ship Fairweather

undertake a project with a crew of NOAA Corps officers, OMAO civilian mariners, and Coast Survey 

scientists.

Although NOS projects occur year-round, the timing of a given project may be limited by seasonal 

environmental conditions of its location. For example, projects in the Arctic or Bering Sea typically take 

place between June and September to avoid dangerous, icy conditions, while projects in the West Coast, 

Northeast, and Mid-Atlantic regions most often take place between March and November. Projects in the 

Southeast or Gulf of Mexico are conducted year-round. The total duration of a project can vary from a 

few days to several months over multiple years. For Coast Survey hydrographic surveys, actual time 

surveying averages approximately 15 days per month over the course of a survey project, although larger 

ships can often survey 20 to 25 days per month under good conditions. When possible, program offices 

coordinate the location and timing of projects to ensure that areas are not unnecessarily repeatedly 

surveyed. This ensures that the potential environmental impacts directly resulting from the projects are 

not exacerbated by repeated surveys within a given area.
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2.3 SCOPE

In this Final PEIS, scope refers to both the geographic and temporal range of the Proposed Action. 

Geographic scope is the spatial extent of the areas potentially affected by the Proposed Action. Temporal 

scope is the timeframe over which the Proposed Action is evaluated. NOS determined the scope of this 

document on the basis of the current extent of NOS project work and the ability of NOS program offices 

to reliably predict their future level of activity. Activities which occur outside of the parameters outlined 

in the below subsections were not considered in the analyses.

2.3.1 Geographic Scope

The “action area” for this Final PEIS encompasses the U.S. territorial sea; the contiguous zone; the U.S. 

Exclusive Economic Zone (U.S. EEZ); rivers; states’ offshore waters; and coastal and riparian lands for 

projects such as the installation, maintenance, and removal of tide gauges. This includes the U.S. portions 

of the Great Lakes and internal waters such as Lakes Tahoe, Mead, Champlain, Okeechobee, and parts of 

major rivers such as the Mississippi, Missouri, Hudson, and Columbia rivers. NOS projects would occur 

within freshwater bodies far less frequently than in marine environments and would likely only occur 

within or near the habitat of most freshwater species on a limited basis or not at all. From 2016 to 2021, 

less than three percent of NOS projects occurred in freshwater. Vessels and uncrewed surface vehicles 

used by NOS may transit through international waters to get to project sites, but no data collection occurs 

in international waters.

The action area assessed in this Final PEIS is organized and analyzed by geographic regions (Figure 2.3-1). 

The regions are:

• Greater Atlantic Region, which includes the U.S. portions of the Great Lakes, New England and the 

mid-Atlantic;

• Southeast Region, which includes the southern portion of the U.S. Eastern Seaboard, the U.S. 

Caribbean Islands (Puerto Rico and the U.S. Virgin Islands), and the Gulf of Mexico;

• West Coast Region, which includes coastal California, Oregon, and Washington;

• Alaska Region, which includes Alaskan waters and the Arctic; and

• Pacific Islands Region, which includes Hawai’i and the Pacific territories of the U.S.
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Figure 2.3-1. Geographic Scope of Final PEIS

2.3.2 Temporal Scope

As with any planning process, the confidence with which an agency can foresee and evaluate its actions, 

and the environmental effects of those actions, decreases at longer time intervals. Changes in spending 

levels, the environment, the data needs of the public, and technologies and field methods available to 

NOS can all change how surveying projects are executed. Based on NOS experience with these factors, 

this Final PEIS analyzes data collection activities for a time period of five years. For the purposes of this 

Final PEIS, a specific project could take place at any time of year.

Consistent with Council on Environmental Quality (CEQ) guidance that “[NEPA documents] that are more 

than five years old should be carefully reexamined to determine if the criteria in Section 1502.9 compel 

preparation of a [NEPA] supplement.” (CEQ, 1981), NOS would reevaluate the Final PEIS to determine if 

the analysis contained within remains sufficient, or if new analysis is required. If necessary, this new 

analysis may take the form of a supplemental PEIS, a new PEIS, or more extensive project-level analysis.

2.4 ACTIVITIES COMMON TO ALL ALTERNATIVES

Under all alternatives, NOS would operate a variety of equipment and technologies to gather accurate 

and timely data on the nature and condition of the marine and coastal environment. In the context of 

project activities, references to NOS include NOS personnel, other NOAA personnel on behalf of NOS, and 

NOS contractors, grantees, partners, and permit/authorization recipients. The subsections below describe 

the technology, equipment, and techniques which would be used in NOS projects regardless of the 
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selected alternative. This Final PEIS would also cover activities not specifically listed below as long as the 

relevant NOS program office(s) determined that the activities are comparable in operating characteristics 

(e.g., similar source level ranges, intensities, and frequencies) and extent of use (e.g., similar likelihood, 

duration, and frequency of use). 

2.4.1 Project-Related Crewed Vessel Operations

Collecting coastal and marine data requires NOS to be able to reach the environments of interest. The 

most common platform for this purpose is a crewed sea-going surface vessel (remotely operated and 

autonomous vehicles are considered in Section 2.4.3). These vessel operations may take place these 

vessels under one of four arrangements:

• The vessel may be operated directly by NOS or by a partner funded under a contract or other 

financial assistance award; 

• The vessel may be operated by OMAO for an NOS project; or

• The vessel may be owned and/or operated by an entity external to NOS under a contract by NOS 

or a partner. These are referred to as “contractor vessels” or “chartered vessels.”

• The vessel may be owned and/or operated by an entity external to NOS under a permit or 

authorization issued by NOS under the National Marine Sanctuaries Act (NMSA). 

Vessels used range from small, unpowered personal watercraft to large research ships. For example, 

Navigation Response Team (NRT) vessels are typically 9-m (28-ft) boats towed by a truck to the general 

project area (Figure 2.4-1). There are also larger vessels such as NOAA Ship Rainier, a 1,600-metric-ton 

(1,800-ton), 70-m (231-ft) hydrographic ship crewed by OMAO officers and sailors (Figure 2.4-2). Ships 

such as Rainier also typically carry one or more “launches” – small boats that are deployed into the water 

directly from the ship. Chartered vessels can be of various sizes and types, depending on the project needs 

and availability. NOS uses the term “ship” for vessels with sleeping accommodations, or berthing capacity, 

that may anchor overnight during a project. NOS uses the term “boat” for vessels without berthing 

capacity that would anchor only in an emergency.

Figure 2.4-1. A Navigation Response Team 

Boat Being Placed in the Water

Figure 2.4-2. NOAA Ship Rainier in

Alaska, with its Survey Launches

Survey vessels would travel to and from project sites and during projects as required. Vessel transit speeds 

vary by location, but are typically lower than 25 knots. Vessels are typically limited to speeds of 13 knots 

during survey activities. Depending on the duration of a project, a vessel might return to port periodically 
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for fuel, supplies, or crew changes. NOS does not routinely have contractor vessels perform long transits; 

local contractors are hired for projects. This document analyzes the environmental impact of all vessel 

transits (i.e., movements) to the project area, during the project, and back to a port for all projects 

undertaken or funded by NOS. Vessel transits and project activities may occur at either day or night. Based 

upon comparison with Global Positioning System (GPS) data collected from automatic identification 

system (AIS) transponders onboard commercial vessels in 2017, vessels used for NOS projects account for 

a very small proportion of U.S. vessel traffic2

. Figure 2.4-3 shows the estimated regional distribution of 

NOS activities for the five-year timeframe of the PEIS based on nautical miles of vessel movement, 

regardless of the selected alternative.

Figure 2.4-3. Geographic Distribution of NOS Crewed Vessel Operations

Based on Five Years of Projected Funding

Note that this Final PEIS does not consider the following:

• Vessel operations that are not related to NOS projects, such as transits to a new homeport or to 

a dry dock, to a non-NOS project, or from a non-NOS project to a port;

• Vessel construction, acquisition, repairs, maintenance, or upgrades, such as the installation of 

new scientific equipment; or

2 Compared to AIS data for commercial vessels in 2017, vessels used or funded by NOS account for 0.3 percent of all nautical 

miles traveled within the U.S. EEZ. However, because AIS transponders are not required for recreational vessels and recreational 

boating data were not available for inclusion in this analysis, vessels used and funded by NOS likely represent orders of magnitude 

less than 0.3 percent of total vessel use within the EEZ.
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• Any chartered vessel operations that are not undertaken as part of an NOS contract or 

cooperative agreement.

These forms of crewed vessel use are neither under NOS control nor connected to NOS projects, and 

therefore are not considered here.

2.4.2 Anchoring

When a vessel is not collecting data, it may anchor either within the project area or nearby. Small boats 

and survey launches used for NOS projects return to port or to the ship each day and do not typically 

anchor, except in an emergency. During any NOS project, a vessel may anchor to avoid adverse weather 

or in the unlikely event of an equipment malfunction, regardless of vessel size. For multi-day efforts, ships 

may anchor within or near the project area to reduce the transit time to the project area and to save fuel.

The choice of anchoring location is at the discretion of the ship’s officers, who select the anchor location 

based on depth, protection from seas and wind, and bottom type. Preferred bottom types are sticky mud 

or sand, as those characteristics allow the flukes of the anchor to dig into the bottom and hold the chain 

in place. NOS would not anchor in known areas of coral, except in an emergency. When working in an unsurveyed area or in an area that has not been surveyed in many years, the ship will try to anchor in bays 

where data have already been collected, providing the ship with better information on where to drop the 

anchor. Existing mooring buoys are used when available. Ships are typically anchored for a time period of 

hours, but during weather events (e.g., tropical storm or hurricane) ships may anchor for multiple days.

2.4.3 Operation of Remotely Operated Vehicles (ROVs), Uncrewed Surface 

Vehicles (USVs), and Autonomous Underwater Vehicles (AUVs)

In addition to crewed vessels, NOS proposes to use remotely operated and uncrewed vehicles to collect 

data. ROVs are controlled remotely at all times by a human operator and are often tethered to a crewed 

vessel. Autonomous vehicles operate with various levels of autonomy and include Uncrewed Surface 

Vehicles (USVs) and Autonomous Underwater Vehicles (AUVs). These systems use a variety of propulsion 

sources, including diesel, diesel/electric, battery, solar, buoyancy driven, and wave-gliding propulsion 

systems.

USVs often look similar to boats, ranging in size from the 1.8-m (6-ft) Teledyne Z-Boat (Figure 2.4-4) to the 

7.7-m (25-ft) USV iXblue Drix (Figure 2.4-5).

Figure 2.4-4. Teledyne Z-Boat Figure 2.4-5. USV iXblue Drix
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AUVs often have a “torpedo”-like appearance, and can range in size from small systems deployed by two 

to three people, such as the 1.7-m (6-ft) REMUS-100 (Figure 2.4-6), or larger systems requiring winches 

or other deployment equipment, such as the 5.5-m (18-ft) REMUS-600 (Figure 2.4-7).

Figure 2.4-6. REMUS-100 AUV Figure 2.4-7. REMUS-600 AUV

2.4.4 Use of Echo Sounders

NOS echo sounders (also referred to as sonars [sound navigation and ranging]) are typically attached to a 

crewed vessel, ROV, USV, or AUV, and are one of the most common categories of active acoustics used in 

ocean navigation, remote sensing, and ocean and habitat mapping. In rare instances, NOS may place echo 

sounders directly on the sea floor or the echo sounders may be operated by divers. 

Echo sounders transmit a repeated series of short sound signals (on the order of milliseconds) into the 

water column. These signals continue until they reach an object of a different acoustic impedance 

(typically the sea floor, but also potentially objects in the water column) and reflect back to the echo 

sounder’s receiver; echo sounders do not transmit while listening for an echo. By measuring the amount 

of time for the sound to return from the sea floor or object, the depth of the water (or the distance to the 

object) can be determined. Echo sounders used for mapping can generally be divided into three 

categories: single beam systems, multibeam systems, and side-scan sonars.

Single beam echo sounderstransmit one focused acoustic beam, typically directly below the vessel (Figure 

2.4-8). Sub-bottom profilers are a specific type of single beam echo sounder, designed to penetrate sea

floor sediments and reveal sub-surface features. The sound energy emitted by the sub-bottom profiler is 

typically of a lower frequency than other echo sounders. These lower frequencies allow the sound signal 

to penetrate the sea floor and reflect back to the vessel when it encounters different types of buried 

sediments and rock (NOAA, 2014a). Single beam systems relied on by NOS, including sub-bottom profilers, 

are typically mounted on the bottom of the vessel hull. 

Multibeam echo sounders transmit a fan of acoustic energy and can resolve individual depths across the 

return beam (Figure 2.4-8). Multibeam systems are the most commonly employed echo sounders for 

mapping the sea floor, as they allow for “full bottom coverage” of the area of interest. Many multibeam 

systems are capable of recording data on acoustic backscatter ‒ data artifacts that may interfere with the 

accuracy of depth soundings. Multibeam backscatter is intensity data collected from multibeam systems 

that can be processed to create low-resolution imagery. Backscatter is co-registered with the bathymetry 
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data and is often used to assist with bathymetric data interpretation. Multibeam systems are typically 

mounted on the bottom of the vessel hull.

Note the greatly improved bottom coverage of the multibeam system which reduces the time 

and number of vessels required to survey a given area. 

Figure 2.4-8. Artist’s Rendering of Single Beam

and Multibeam Echo Sounder Operation

Side-scan sonars (sometimes referred to as “imaging sonars”) are a specialized system for detecting 

objects on the sea floor that typically use fans of acoustic energy to look down and to the side of the 

sensor platform (Figure 2.4-9). In a side scan, the transmitted energy is formed into the shape of a fan 

that sweeps the sea floor from directly under the unit to either side, typically to a distance of 100 m (328 

ft). The strength of the return echo is continuously recorded, creating a "picture" of the ocean bottom 

(Figure 2.4-10). For example, objects that protrude from the bottom create a light area (strong return) 

and shadows from these objects are dark areas (little or no return). Side-scan systems are either mounted 

underneath the vessel or towed behind the vessel on a cable (NOAA, 2018b).
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Figure 2.4-9. Diagram of Side

Scan Sonar Operation

Figure 2.4-10. A Side Scan Sonar Image of 

Herbert D. Maxwell, a Schooner that Sank 

in the Chesapeake Bay on May 16, 1910

Different echo sounders are designed to produce sound at different frequencies. Single beam echo 

sounders used by NOS can range from 0.5 kHz up to 200 kHz or more. Multi-beam echo sounders used by 

NOS typically range from 12 kHz up to 900 kHz or more. Side scan sonars used by NOS typically range from 

300 kHz to 1600 kHz.

In general, higher-frequency echo sounders provide higher precision than lower frequency systems. 

However, because higher frequency sound is absorbed in seawater much faster than lower frequencies, 

high frequency systems are limited in range and are therefore used in shallower water. Lower frequency 

echo sounders, by comparison, are typically used in deeper water. The source level of these echo sounders 

can range as high 247 decibels (dB) re: 1 microPascal (μPa) m.3

2.4.5 Use of Acoustic Doppler Current Profilers (ADCPs)

Acoustic Doppler Current Profilers (ADCPs) are active acoustic systems used to measure the velocity of 

water by measuring the relative shifts in sound frequency (i.e., the Doppler shift) associated with relative 

motion. These profilers provide detailed and important data on oceanographic conditions, including 

current patterns, waves, and turbulence. ADCPs (Figure 2.4-11) are often operated from tethered 

systems, buoys, or fixed moorings. Mobile ADCPs are hull mounted. The majority of these systems used 

by NOS operate at high to extremely high frequency (75-1,200 kHz) and are moderate in terms of source 

levels (< 160-180 dB re: 1 μPa m).

3 Here and throughout this document, source levels are expressed in decibels with a reference pressure of 1 

micropascal (dB re: 1 μPa m).
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Figure 2.4-11. Example of Subsurface ADCP Buoys Currently in Use by NOS

(shown: Streamlined Underwater Buoyancy System Model A2 Coastal ADCP)

2.4.6 Use of Acoustic Communication Systems

Many underwater devices and platforms communicate with one another by emitting and receiving sound, 

such as simple “pingers”, altimeters, and acoustic telemetry systems, including acoustic modems. Pingers 

are typically used to indicate the location of an underwater device and have short-duration chirp signals 

in the 10s of kHz range at moderate source levels (160 to 180 dB re: 1 μPa m). Acoustic modems may 

include encoded (modulated) signals relaying navigational or operational data more easily which can then 

be decoded by receivers. These systems are commonly used in sub-surface operations, between remotely 

deployed buoys, in navigational channels, or on sub-surface vehicles. Because they are commonly used to 

communicate data over km or greater ranges, NOS typically uses mid-frequency ranges (10s of kHz) at 

moderate to relatively high source levels (160 to 200 dB re: 1 μPa m). Sound Velocity Profilers are active 

acoustic devices that measure sound speed for echo sounding corrections using the two-way travel time 

of a very high frequency sound signal across a short distance.

2.4.7 Use of Sound Speed Data Collection Equipment

NOS collects sound speed data throughout mapping surveys to determine the speed of sound in the water 

column at a given location and time, which allows crews to correct for refraction errors in the echo 

sounder data. Taken together, the two-way travel time of the acoustic signal from a single beam or 

multibeam echo sounder and the speed of sound in water determine sea floor depths.

Sound speed data are collected periodically in one of three ways. In the first method, every one to four 

hours a survey technician slowly lowers a sound speed profiler ‒ known as a CTD instrument – from a 

stationary vessel to the sea floor and back (Figure 2.4-12). Passive collection of conductivity, temperature, 

and depth with CTD systems involves remote sampling of these parameters that are used in 

oceanographic sampling and to inform site-specific sound propagation models. CTDs do not produce and 

measure sound, but rather measure environmental conditions that can be used to reconstruct how sound 

propagates through the water column.

A second method involves a moving vessel profiler, which is automatically lowered and raised through the 

water column at regular intervals while the vessel is in motion (Figure 2.4-13). Mobile vessel profilers are 

submerged for time periods ranging in minutes.
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Figure 2.4-12. CTD Instrument Figure 2.4-13. Moving Vessel Profiler

Mounted on the Fantail of a Ship

A third method is the use of expendable bathythermographs (XBTs) for profiling the water column. An 

XBT is a probe dropped from a ship that measures the temperature as it falls through the water (Figure 

2.4-14). A resistance in the head of the probe and a very thin twin-wire, connecting the probe to the 

equipment on the ship, compose the electronic circuit for measuring the water temperature. The probe 

is designed to fall at a known rate, so that the depth of the temperature profile can be inferred from the 

time since it entered the water. Deployments can be made using manual or automatic launchers (Figure 

2.4-15). 

When XBTs are used, a small portion of the probe (5 to 8 centimeters [cm] (2 to 3 inches [in]) long and 

approximately 0.7 kilograms (kg) (1.5 pounds [lbs]) remains on the sea floor. The probes, constructed of 

metal and plastic, fall to the sea floor and detach from the connecting line. The connecting line then 

retracts back to the vessel. 
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Figure 2.4-14. XBT Probe Figure 2.4-15. XBT Hand Launcher

2.4.8 Operation of Drop/Towed Cameras and Magnetometers

NOS uses drop/towed cameras for delineation and identification of sea floor habitats (i.e., ground 

truthing) through visual observations. Magnetometers, passive instruments which measure changes in 

the magnetic field of the earth, also are commonly drop/towed to survey cultural heritage sites and to 

geologically characterize the sea floor. Drop/towed cameras and magnetometers are launched from the 

ship or small boats and lowered on a cable using a power winch or by hand using a line. Drop/towed 

cameras and magnetometers are tethered at all times and are operated at approximately 1 m (3 ft) above 

the sea floor usually on predetermined transects. The total time of equipment submersion varies by 

project, but typically occurs on the scale of hours. 

2.4.9 Collection of Bottom Grab Samples

Some NOS surveys require the collection of sea floor sediment samples by lowering a grab sampler at a 

rate of about 1 m per second (3 ft per second) through the water column to the sea floor. Bottom samples 

are collected for a variety of reasons (for example, selecting anchorages, ground truthing the sea floor, 

and verifying benthic habitat maps). Typically, crews use a clamshell bottom snapper (6” by 6”) or similar 

type of grab sampler or sediment corer to obtain samples of the surface sediment layer (approximately 

the first 5 cm (2 in) of sediment). As the sampler is lowered, two hinged upper lids swing open to let water 

pass through. When the sampler reaches the bottom, the overlapping spring-loaded scoops are tripped 

on the line, and the lids close to contain the sediment and prevent sample washout. Corers such as box 

corers work similarly but can sample different volumes and depths of sediment. Depending on the goals 

of a particular project, the sediment sample is collected, analyzed, and photographed, and under some 

circumstances released from the sampler underwater.

Samples are characterized by color, type of bottom material and other characteristics. Field personnel 

may have a bottom sample plan as a guideline of sampling density, but sampling can also occur based on 

ground-truthing needs identified in the mapping products, and researchers are given discretion on the 
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exact location of sampling. Crews do not typically collect samples in waters deeper than 80 m (262 ft). 

Additionally, in areas surveyed within the last 30 years, the surveyor might not need to collect samples at 

all. In some cases, the surveyor can use backscatter or side scan data acquired during the survey operation 

to determine the best place to sample. Grab samples may also be used for current survey site 

reconnaissance. 

2.4.10 Use of Passive Listening Systems

Passive listening systems are hydrophones that receive sounds present in the environment from either 

natural sources or active acoustic systems. These systems do not produce sound but record it for 

monitoring and research purposes. Passive listening systems are often integrated into the housing of 

other equipment, such as ADCPs, or moored in place to the sea floor. NOS does not use expendable 

passive listening systems. 

2.4.11 SCUBA Operations

Some projects include deploying SCUBA divers. NOS conducts SCUBA operations to verify and validate 

benthic habitat classifications, collect samples, conduct fish and benthic habitat surveys, or install or 

retrieve small sensors or other scientific instrumentation, including installation of tide gauges. In-water 

diver activities include benthic and fish monitoring that would be conducted usually on hard bottom and 

coral reef habitats and near cultural and historic resources such as shipwrecks. 

Divers are deployed from crewed vessels, typically small boats, and traverse small areas in support of 

specific tasks. The majority of NOS dives are performed by CO-OPS and Coast Survey for tide gauge

installation, maintenance, or removal (73 percent), which requires relatively quick dives that are only a 

small component of the entire installation process. Twenty-one percent of NOS dives are performed by 

the Office of National Marine Sanctuaries (ONMS); the National Centers for Coastal Ocean Science

(NCCOS) and Office of Response and Restoration (ORR) together account for the remaining six percent. 

2.4.12 Installation, Maintenance, and Removal of Tide Gauges

A tide gauge is a device fitted with sensors that continuously record the height of the surrounding water 

level. These data are critical for many coastal activities, including safe navigation, sound engineering, and 

habitat restoration/preservation. Local and national networks of tide gauges measure water levels, 

provide the vertical reference system required to describe water level variations, and help develop tidal 

predictions. A tide gauge measures the changes in water levels and transmits the data by satellite to a 

computer database for processing. The tide gauge station consists of a sensor, data collection platform, 

solar panels, and satellite transmitter. The four types of gauge conformations listed below are the most 

commonly used by NOS:

• An acoustic sensor uses sound waves to measure the distance between the sensor and the water 

level surface (Figure 2.4-16). It is most often used when an existing pier or dock is available on 

which to mount the sensor and includes a protective well that houses the sounding tube. These 

sensors typically emit 1.05 kHz acoustic signals at low source levels (-45 dB re: 1 μPa m). Both 

short-term and long-term acoustic tide gauges include some or all of the following nonpermanent equipment: tide house (located on a pier), data collection platform, sensor (typically 

an “aquatrak”) housed in a 30” x 30” portable plastic case, benchmarks, and satellite transmitter 

(tripod station with antenna and solar panel). A long-term acoustic tide station typically includes 

some or all of the following equipment: primary and backup water level sensors; primary and 

backup data collection platforms; a Geostationary Operational Environmental Satellite (GOES) 
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transmitter and antenna; GPS antenna; batteries; solar panels; water temperature sensors; mast 

or tower on which to mount wind sensors; barometric pressure sensor; and air temperature 

sensor. The acoustic sensor requires a 6-inch-diameter polyvinyl chloride protective well to house 

the sounding tube; the well is attached to the pier with stainless steel brackets to maintain sensor 

stability. 

• A pressure sensor measures the pressure of the water column above an underwater orifice that 

is securely attached to maintain its position (Figure 2.4-17). It is used when there is little 

infrastructure available or as a backup sensor. A constant supply of air is pumped through a tube 

to the orifice to establish a zero point from which to measure the changes in pressure in the water 

column.

Figure 2.4-16. Pier-mounted 

Acoustic Sensor Tide Gauge Station

Figure 2.4-17. Pressure Sensor Tide

Gauge Station (and Tubing)

• A microwave water level radar sensor (MWWL) uses radar waves to measure the distance from 

the sensor to the water (Figure 2.4-18). It is used when the existing infrastructure allows its 

installation in a location overlooking the water surface. This is the only type of sensor that is not 

in direct contact with the water. Station components may include some or all of the following 

equipment as noted in the acoustic sensor above: primary and backup water level sensors; 

primary and backup data collection platforms; a GOES transmitter and antenna; GPS antenna; 

batteries; solar panels; water temperature sensors; mast or tower on which to mount wind 

sensors; barometric pressure sensor; and air temperature sensor.

• A GPS tide buoy employs a GPS receiver that measures both horizontal and vertical position using 

GPS technology (Figure 2.4-19). It is used primarily during hydrographic surveys to obtain data in 

remote locations without existing infrastructure on which to mount a gauge. Some buoys may 

also be used to collect current data observations with a mounted acoustic sensor in an identified 

region. These buoys are acoustic mounted sensors on either an existing navigation buoy (i.e., 

owned by the U.S. Coast Guard [USCG]) or buoys deployed with ADCPs as noted in Section 2.4.5. 

They are also used to collect data in shipping channels. Examples of tide buoys are the two 

HydrolevelTM GPS tide buoys currently owned by the Coast Survey Development Laboratory. They 

are approximately 26” in diameter, weigh 58 kgs (128 lbs), have amber USCG light emitting diode 

(LED) lights visible from 3 miles away, and use sealed lithium batteries. A typical mooring 

configuration includes 45 to 68 kgs (100 to 150 lbs) of anchoring mass (usually a combination of a 
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23-kg (50-lb) primary anchor and several 7-kg (15-lb) “mushroom” anchors) and a heavy chain, 

with a total footprint of approximately 1 square meter (3 ft).

Figure 2.4-18. Microwave Sensor

and Instrument in Bridgeport, Connecticut

Figure 2.4-19. A GPS Tide Buoy

Although some of these tide gauges are operated only for the duration of a single project, most NOS tide 

gauges belong to a larger network of more permanent gauges. NOS (through CO-OPS) manages a 

permanent observing system of over 200 long-term, continuously operating data-collection platforms 

called the National Water Level Observation Network (NWLON). The NWLON measures tide levels and 

other oceanographic and meteorological parameters. The observing stations contribute to NOAA’s 

forecast models which provide tsunami and storm surge warnings. Some tide gauge stations also include 

additional co-located sensors, such as High Frequency Radar Systems (HFR), which collect currents data 

and support currents prediction models collected by boat or mounted ADCPs.

Approximately one quarter of the NWLON is located in the Great Lakes (non-tidal), providing water level 

data for the international management of those water resources. The NWLON provides the national 

standards for tide and water level reference datums used for nautical charting, coastal engineering, 

international treaty regulation, and boundary determination. CO-OPS also installs and operates 

approximately 100 short-term water level stations annually in support of a variety of programs including 

hydrographic and shoreline mapping projects, marine boundary determination, real time navigation 

systems, coastal habitat and marsh restoration projects, and other projects (NOAA, No Date-e). 

2.4.12.1 Tide Gauge / Tide Buoy Installation

Tide gauge installation occurs primarily out of the water. Tide gauges are typically secured to existing 

piers, docks, and bulkheads. Rocks are the most common natural structures used to secure sensors in 

remote locations for short-term stations. Equipment includes primary and backup systems for sensors, 

data processing, and data transmission. All equipment is installed to last several years before needing 
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service or replacement. Short-term stations typically involve one primary system with no backups. They 

are less extensive, easier to install and remove, and usually only stay in place for the length of the data 

collection period (1 to 3 months). Geodetic “benchmarks” must be installed near each water level station 

and are long-term reference points to which the tidal datums can be related through standard surveying 

techniques.

A long-term station requires a network of ten benchmarks to “level” to the tide gauge during operations, 

while a short-term station only requires five benchmarks. The larger number of marks required for a longterm station is proportional to the investment made over time in the data collection and tidal datums 

determined. Additional marks ensure that there are at least five marks, even if future construction 

destroys several marks at once. The benchmarks are spaced at least 61 m (200 ft) apart to strengthen the 

leveling data and reduce the chance of losing several marks at a time. They are typically established in a 

variety of permanent structures, including surface markers, or deep driven stainless-steel rods when 

existing structures are not available.

A field crew of three to six people installs the equipment. Crews travel to most gauge sites over land, but 

a few locations ‒ especially in remote areas of Alaska ‒ can only be reached by boat, seaplane or 

helicopter. Installation equipment includes both hand and power tools. When a tide gauge is installed on 

land it is located beyond the mean high tide line, so any disturbed sediments from installation do not 

reach the water.

During tide buoy installation, a buoy is tethered to the anchoring hardware with a 15-m (50 ft), 2.5-cm (1-

in) diameter rubber cord, followed by a section of 0.5-cm (3/16-in) Amsteel rope. The rubber cord attaches 

to the bottom of the buoy, and the rope attaches the rubber cord to the anchor. The combined length of 

the rubber cord and the rope exceeds the nominal water depth by a factor of approximately two (i.e., 

“mooring scope”). The GPS buoy is deployed by floating the buoy away from the vessel to the extent of 

the rubber cord and rope. The anchor is then lowered slowly to the point where the rope attaches to the 

rubber cord, at which point the anchor is released. Tide buoys are typically operated for one month before 

being removed.

2.3.12.2 Tide Gauge / Tide Buoy Maintenance

Once installed, tide gauges operate autonomously, collecting data on water levels and transmitting the 

data by satellite to a computer database for processing. The gauge operates under its own power -

typically solar, sometimes with a battery back-up. Short-term stations may be operational for as little as 

one month, or they may operate for up to one year. Personnel would return to the long-term stations 

periodically for water level measurements and maintenance, typically once per year. Maintenance visits 

would also be used to equip existing tide gauges with MWWL sensors and upgraded weather/stormproofing. 

Very little maintenance of tide buoys is required. NOAA tide buoys are programmed to send out a "health 

message" email to a predetermined distribution list at regular intervals via satellite. For example, Coast 

Survey tide buoys send messages hourly. If the buoy reports its position outside of a certain radius (“watch 

circle”), it issues a separate alert. Field personnel respond to situations where the buoy breaks its mooring 

or stops sending messages. Occasionally the batteries must be replaced or recharged, and field personnel 

must retrieve the buoy with a small boat and bring it back to the ship or shore. When they bring the buoy 

on board, the team attaches a temporary float to the end of the mooring so that it can be reused after 
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the buoy batteries have been refreshed. At the end of the survey, the field personnel recover all 

components of the buoy. 

2.4.12.3 Tide Gauge / Tide Buoy Removal

Long-term stations, such as those of the NWLON, remain in operation indefinitely. They receive a 

preventative maintenance visit once a year that involves a standard inspection of all equipment, leveling 

from sensors to benchmarks to determine sensor stability, GPS observations, and diving operations to 

inspect the underwater components if present. Emergency repair visits would address failed components. 

Temporary gauges would only be repaired in the event of a specific equipment failure.

Once a temporary tide gauge is no longer needed, field personnel would be sent to remove the gauge. 

Personnel level the gauges when they remove them. SCUBA diving may or may not be involved, depending 

on the location and the type of sensor installed. Field personnel would also remove a long- or short-term 

gauge upon project completion. All equipment is removed from the site, although the benchmarks would 

remain as established spatial reference points. To recover a tide buoy, the buoy float is brought aboard 

the vessel along with the length of rubber cord. The total anchoring hardware is then hauled in by rope.

2.4.13 Installation of GPS Reference Stations

NOS installs GPS reference stations to support ellipsoidally referenced surveys, where height and depth 

are measured with respect to a geodetic datum (“ellipsoid”) rather than to a tidal datum. Ellipsoidally 

referenced surveys improve the efficiency of hydrographic surveys by removing the requirement for 

concurrent water level observations and hydrographic survey data collection.

Equipment used in ellipsoidally referenced surveys includes a ship-based inertially-aided GPS system and 

a shore-based GPS reference station. If an existing network, such as the Continually Operating Reference 

Stations, is not available, field personnel must establish a new network by using a tripod, an antenna, a 

receiver housed in a hardened waterproof “suitcase,” and data storage connected to a radio modem for 

remote downloads. If electrical service is not available at the reference station site, the network system 

requires a set of 12-volt marine, deep-cycle rechargeable batteries and a solar panel array. The site chosen 

on shore must provide an obstruction-free view to GPS satellites and accommodate line-of-sight radio 

communications. No equipment maintenance is required, although if no remote data download capability 

is available, field personnel must visit the site periodically to download data vital for survey processing.

2.5 ALTERNATIVES A, B, AND C

NOS identified a “No Action” alternative (Alternative A), which represents the actions and resulting effects 

that would occur given continued coastal and marine data collection at current levels of effort using 

current technology and methods (i.e., the status quo), and two action alternatives (Alternatives B and C) 

that satisfy the purpose and need for the action as outlined in Section 1.3. These alternatives use many of 

the same technologies, equipment, and methods for surveying and mapping (as described in Section 2.4) 

and differ from each other primarily in their overall level of survey effort. 

2.5.1 Alternative A: No Action - Conduct Surveys and Mapping for Coastal and 

Marine Data Collection with Current Technology and Methods, at Current 

Funding Levels

CEQ regulations (40 Code of Federal Regulations [CFR] 1502.14) require the assessment of the No Action 

alternative in Environmental Impact Statements. The No Action alternative provides the baseline 
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condition of the existing environment from which to compare all other alternatives. In the case of an 

ongoing agency action, the No Action alternative represents adherence to current management direction 

or intensity. 

Under Alternative A, NOS would continue to conduct the activities listed in Section 2.4 to gather accurate 

and timely data on the nature and condition of the marine and coastal environment. This alternative 

reflects the technology, equipment, scope, and methods currently in use by NOS, at the level of effort 

reflecting NOS fiscal year 20194 funding levels. The level of activity for Alternative A is described in Table

2.6-1 in terms of nautical miles of survey effort and the overall number of projects that would continue 

to occur using each activity. 

2.5.2 Alternative B: Conduct Surveys and Mapping for Coastal and Marine Data 

Collection with Equipment Upgrades, Improved Hydroacoustic Devices, 

and New Tide Stations - NOS Preferred Alternative

NOS constantly seeks to improve the design and implementation of coastal and marine data collection. 

Alternative B therefore consists of Alternative A plus the more widespread adoption of new techniques 

and technologies (such as ROVs, MWWL sensors, etc.) to more efficiently perform surveying, mapping, 

charting and related data gathering. The introduction of these technologies, combined with continued, 

more traditional data collection methods, would allow NOS to perform more projects covering more 

survey miles annually than would be possible under Alternative A. Specific examples of adaptive methods 

and equipment that NOS programs are likely to promote, plan for, and adopt under Alternative B in the 

next five years include:

• Greater use of ROVs with echo sounder technologies;

• Greater use of AUVs with echo sounder technologies;

• Conversion of one or more existing 10-m (33 ft) crewed survey boats into USVs;

• Greater use of more efficient, wide-beam sonar systems (phase-differencing bathymetric 

systems) for nearshore hydrographic surveys;

• Expanded geographic distribution of projects that use hydroacoustic sampling methodologies;

• Increased field operations in the National Marine Sanctuary system with associated requirements 

for hydroacoustic charting, surveying, mapping and associated activities; and

• Installation, operation, and maintenance of additional water level stations by CO-OPS, including 

transitioning to mostly MWWL sensors and upgraded storm strengthening to make stations more 

climate resilient.

Under Alternative B, all of the activities described in Alternative A would continue, many at a higher level 

of effort. The nature of these actions would not change from those described above in Section 2.4, but 

the overall level of activity would be increased as described in Table 2.6-1.

NOS identified Alternative B as the preferred alternative because it takes advantage of newer, more 

efficient technology, provides increased support for national marine sanctuaries, and more effectively 

addresses the nation’s needs for coastal and marine data.

4 NOS is using 2019 as the baseline year for funding, as that was the last year of normal NOS operations prior to 

COVID-19 disruptions. 
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2.5.3 Alternative C: Upgrades and Improvements with Greater Funding Support

Like Alternative B, Alternative C adopts new techniques and technologies to encourage greater program 

efficiencies regarding surveying, mapping, charting, and related data gathering activities. In addition, 

Alternative C would consist of NOS program implementation with an overall funding increase of 20 

percent relative to Alternative B.

Under Alternative C, all of the activities described in Alternative B would continue, many at a higher level 

of effort. The nature of these actions would not change from those described above in Section 2.4, but 

the overall level of activity would be augmented as described in Table 2.6-1.

2.6 COMPARISON OF ALTERNATIVES

In order to compare the alternatives, NOS collected data on the projected number of projects and 

activities that would be conducted annually by its program offices under the three alternatives selected 

for analysis. In some cases, the exact number of times an activity would take place is not known in 

advance. For example, a crew’s decision to deploy an anchor is based on schedule constraints, fuel 

supplies, safety, weather, availability of anchorages, and other concerns. Similarly, the decision to deploy 

a sound speed data collection instrument can be contingent upon data gathered during the survey itself. 

Therefore, these activities were enumerated by the number of projects where the equipment would be 

expected to be used based on a review of previous NOS projects. This approach allows the reader to 

compare the prevalence of these activities by alternative, as shown in Table 2.6-1.

It is also important to note that project estimates for each activity were reported by NOS program offices 

non-exclusively. As noted in Section 2.2, a single project typically consists of multiple activities. For 

example, a single Coast Survey project may include the activities of vessel operation, echo sounder 

operation, anchor deployment, and sound speed data collection. Non-exclusive reporting allows for more 

robust comparisons of activities between the alternatives, but it results in a greater total number of 

projects reported from that which would actually occur. For example, one nautical mile of data collection 

for a mapping survey project is reported as both one mile of the “crewed vessel use” activity and one mile 

of the “echo sounder use” activity, as the vessel and the echo sounder are operated simultaneously. As 

another example, many tide gauge installation projects would be counted as both a tide gauge installation 

activity and as a SCUBA dive activity, as the installation of many gauges requires diving to install the 

pressure gauge component of a tide gauge.

While both the total number of nautical miles surveyed by crewed vessels and the discrete number of 

projects increase by approximately 10 percent between each subsequent alternative, the magnitude of 

individual activities does not increase uniformly between alternatives, reflecting priorities in funding 

allocation and technology use. For example, ROV/USV/AUV use increases 201.7 percent from Alternative 

A to B and 18.5 percent from Alternative B to C. The proportionally greater increase in ROV activity 

compared to that of overall crewed vessel activities demonstrates the building movement towards 

uncrewed survey activities and the overall commitment of NOS agencies towards methodological 

innovation and efficiency. Likewise, mobile ADCP use increases 90.2 percent from Alternative A to B and 

35.7 percent from Alternative B to C, also reflecting NOS commitment to improved technology and 

efficiency.

It is important to note that the high number of SCUBA operations reported is related to the high number 

of tide gauge installation/maintenance/removal projects, as the majority of SCUBA projects 
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(approximately 73 percent) are tide gauge projects. Tide gauge projects usually involve short SCUBA dives 

that are not a large component of the overall project. 
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Table 2.6-1. Comparison of Annual NOS Planned Surveying

and Mapping Activities under Alternatives A, B, and C

Activity

Described 

in Section Alternative A

Percent Increase 

from Alternative A 

to Alternative B Alternative B

Percent Increase 

from Alternative B 

to Alternative C Alternative C

Crewed vessel 

operations

2.4.1 518,000 nm 

(959,000 km) 

11.4% 577,000 nm 

(1,070,000 km) 

10.4% 637,000 nm 

(1,180,000 km) 

Anchoring** 2.4.2 55 projects 6.9% 59 projects 8.1% 64 projects 

ROV/USV/AUV

movement

2.4.3 28,600 nm (53,000 

km)

201.7% 86,300 nm 

(160,000 km)

18.5% 102,300 nm 

(189,000 km)

Use of echo sounders 2.4.4 479,000 nm 

(887,000 km)

11.5% 534,000 nm 

(988,000 km)

10.3% 589,000 nm 

(1,090,000 km)

Use of sub-bottom 

profilers

2.4.4 3,210 nm (5,940 

km)

65.4% 5,310 nm (9,830 

km)

45.2% 7,710 nm (14,300 

km)

Use of mobile ADCPs 2.4.5 5,890 nm (10,900 

km)

90.2% 11,200 nm (20,700 

km)

35.7% 15,200 nm (28,200 

km)

Stationary ADCPs 

installed/visited for 

maintenance/removed

2.4.5 37 installed/78 

maintenance 

visits/33 removed

5.4%/1.3%/0% 39 installed /79 

maintenance visits 

/33 removed

2.6%/0%/0% 40 installed /79 

maintenance visits 

/33 removed

Use of acoustic 

communication 

systems

2.4.6 24 projects 37.5% 33 projects 18.2% 39 projects

Sound speed data 

collection

2.4.7 56 projects 14.3% 64 projects 10.9% 71 projects

Drop/towed camera 

operation

2.4.8 31 projects 16.1% 36 projects 13.9% 41 projects

Bottom sample 

collection

2.4.9 54 projects 13.0% 61 projects 11.5% 68 projects

Use of passive listening 

systems***

2.4.10 21 projects 14.3% 24 projects 20.8% 29 projects

SCUBA operations 2.4.11 248 projects 2.4% 254 projects 5.9% 269 projects
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Activity

Described 

in Section Alternative A

Percent Increase 

from Alternative A 

to Alternative B Alternative B

Percent Increase 

from Alternative B 

to Alternative C Alternative C

Tide gauges 

installed/visited for 

maintenance/removed

2.4.12 32 installed /305 

maintenance visits 

/30 removed

15.6%/0%/16.7% 37 installed /305 

maintenance visits 

/35 removed

8.1%/0%/8.6% 40 installed /305 

maintenance visits 

/38 removed

GPS reference system 

installation

2.4.13 12 installed 8.3% 13 installed 15.4% 15 installed

*All numbers are approximate and represent an annual level of effort. Projects for each activity were reported by NOS agencies without respect to the 

combination of activities within projects (e.g., a project involving both crewed vessel operation and echo sounder use would be reported as one crewed vessel 

project and one echo sounder project).

**NOS estimates that 20 percent of crewed vessel projects include an anchoring component.

***In addition to the projects presented in the table, CO-OPS uses passive listening systems on an as-needed basis. This entails the use of transponder or 

interrogator sensors during the deployment or retrieval of ADCPs.