Leveling Program Surveying

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Accurate models of storm surge and pollution, highway planning, effective resource management, and adequate disaster preparedness all require accurate elevations. As far back as 1817, the Survey of the Coast began determining elevations in coastal areas using trigonometric methods. Determination of very accurate elevations with instruments that were based on a bubble in a vial of liquid, called spirit leveling, replaced the less accurate trigonometric methods over time. NOAA's National Geodetic Survey continues its elevation work today, adding cutting-edge technology such as the global positioning system to its surveying toolkit.

Knowledge of elevations is critical to surveyors, engineers, coastal managers, developers, and those who make resource or land-use management decisions. NOAA’s National Geodetic Survey (NGS) provides a great deal of the accurate elevation data needed by these groups to do their work successfully. However, sea level rise, subsidence (i.e., land sinking), and geological events such as earthquakes are among the many forces constantly changing the surface of the Earth. NGS responds to these changes and to changes in technology by working to develop and refine fast and accurate methods of data collection and to transfer new knowledge and techniques to the surveyors with whom the agency works in partnership.

Program Details. The land surveying & mapping technology program prepares students to enter a high-tech profession that uses state-of-the-art equipment to determine the location and measurement of improvements and other physical features above or below the earth s surface. Surveying is an integral compo­nent for land development by civil engineers, mu­nicipal planners, and the construction industry. Surveying studies are offered for both an AAS degree and BS degree. Our four year surveying program is the only ABET accredited degree in New York and is only one of four in the northeast. If you're looking for an active and well compensated career, consider surveying and geomatics engineering technology. Leveling surveys typically performed by the Department. For details regarding standards, refer to Chapter 5, “Accuracy Classifications and Standards.” The Department’s differential leveling survey specifications shall be used for all Caltrans-involved transportation improvement projects, including special-funded projects. Each level of training prepares a student for dif­ferent levels of certifications that are becoming highly valued by employers in the surveying industry. The Land Surveyor certificate covers the core concepts and prepares a student to take the NSPS Level II and Level III Certification for the Survey Technician.

This party is using a Fischer level to leap frog its way into Glen Canyon in 1921. Click image for larger view.

The most accurate elevation data are collected through a process called “spirit leveling,” which is performed with an instrument that is a combination of a telescope and a spirit level vial. Called a level, the instrument is used to read values from a set of specially constructed and marked rods. Leveling involves determining differences in elevation between survey points following a “leap frog” approach. Building off of known elevations and carrying elevations forward from point to point with a level and rods, surveyors construct a “level line.”

Level lines are marked by periodically placing benchmarks in the ground along the line. NGS has been in the business of leveling since the 1800s, and has placed hundreds of thousands of benchmarks across the U.S. These benchmarks are a fundamental component of the National Spatial Reference System.

As a leader in providing data and developing and using surveying technologies, NOAA continues to update elevation data across the country. This article is a brief journey through the history of leveling and its applications.

The Early History of Leveling

The science of leveling goes back to the ancient Greeks, Egyptians, and Romans and their massive construction projects. Early leveling methods used water in a container to obtain sightings that were parallel with the ground, or “level.” In the mid-1600s, Melchisedech Thevenot sealed water in a vial in such a way as to form a bubble. This vial provided the basis for the surveyor’s level developed 100 years later. A surveyor's level combines a telescope having cross-hairs with a level vial.

A “spirit level” uses fluids such as ethanol and sulphuric ether in the leveling vial rather than water. Their lower freezing point minimizes the variations in measurements due to changes in temperature and prevents freezing. Image courtesy of Dieter Schmid Fine Tools, Berlin, Germany.

Eventually, the alcoholic “spirit” ethanol replaced the use of water in the vials because of ethanol’s lower freezing point. Called a “spirit level,” this bubble floating in a vial of fluid is at the core of both the common carpenter’s level readily found in hardware stores today and the precision equipment used by NGS and its predecessor agencies, as well as other surveyors and engineers, to determine elevations by leveling.

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Geodetic leveling differs from ordinary spirit leveling in that it requires more sensitive instruments, specific techniques, and more care in making observations. Geodetic leveling also incorporates computations that remove errors due to the environment and instruments and that account for the curvature of the Earth. NGS and its predecessor agencies, including the Coast Survey, have been involved in geodetic leveling since the mid-1800s.

The First Geodetic Level Lines

Although spirit levels are mentioned in historic documents as early as 1854, the Coast Survey’s first recorded use of spirit levels to survey a geodetic-quality level line was as part of a study of the tides and currents of New York Bay and the Hudson River in 1857. Using spirit levels, G. B. Vose connected a series of tide gauges from New York City to the Albany area, proceeding with such care that in one section across a long bridge,' it was necessary to run over the work five times.” Tide station GRISTMILL was established from this work and provided the mean sea level datum upon which the U.S. Lake Survey later based the elevation of water surfaces on the Great Lakes.

In 1871, Congress gave the Coast Survey (which would be renamed the Coast and Geodetic Survey (C&GS) in 1878) a specific geodetic function in addition to its charting function. Following this new mandate, the Survey began planning for a transcontinental arc of triangulation following the 39th parallel or degree of latitude. This project required the most accurate elevations to date, and thus the craftsmen of the Coast Survey’s instrumentation section designed and constructed a new and more precise level.

This instrument, a wye level from around 1877, has a “striding” level – a level vial sitting astride the telescope and mounted on the same Y yokes as the telescope itself. The distance between the level and the telescope created errors caused by temperature variation. Click image for larger view.

The new instrument was a “wye” level, so called because the telescope rested in Y-shaped supports. It sighted on a target clamped to a level rod. Use of the instrument and rods was slow and cumbersome, requiring numerous computations to correct for various factors. Nonetheless, between 1877 and 1900, more than 5,590 miles (9,000 kilometers) of leveling were completed along the 39th parallel.

The 39th parallel leveling began in October 1877 with the establishment of “Benchmark A” in the foundation wall of the Washington County Court House in Hagerstown, Maryland, where it can still be seen today. A level line was then run from the courthouse along the nearby turnpike to the aquaduct carrying the C&O Canal over Conococheage Creek near Williamsport, Maryland. As the observing seasons passed, the level line followed the C&O Canal to its end at Cumberland, Maryland, and then continued westward along railroad tracks.

BENCHMARK A in Hagerstown, Maryland. Click image for larger view and image credit.

As this first level line was carried west, other level lines were connected to tide gauges and run along rivers like the Mississippi and Arkansas and along various railroad lines, eventually connecting to the 39th parallel transcontinental line. Completed in the first decade of the 1900s, this leveling network not only enhanced the transcontinental survey, it also provided benchmarks at frequent intervals for engineers and surveyors in need of accurate elevations for local projects.

Evolving Levels

The Fischer level had a level vial within the telescope tube and allowed the observer to read the rod and level bubble simultaneously. The level also eliminated a complicated system of micrometer readings and calculations. Click image for larger view.

In 1899, a committee compared C&GS leveling to that of the U.S. Army Corps of Engineers and the U.S. Geological Survey in order to evaluate accuracy, cost, and speed. The study revealed a systematic error in the C&GS leveling, probably caused by the effect of changes in temperature on equipment and by settling of the instruments and rods during the long period of time required to make observations.

As a result of the committee findings, E. G. Fischer designed a new instrument, the Fischer level, which was to remain the workhorse of C&GS leveling until the 1960s. The new level, built of an iron-nickel alloy, was minimally affected by temperature variations and also allowed for a change in observation methods that decreased the time necessary for observations.

Technology has evolved from the telescope and level vial of early leveling instruments to the space-age look of the DNA03, shown above.

Around 1950, technological advancements produced automatic, or self-aligning, levels and digital readouts. These new levels led to an eventual replacement of the Fischer-style level with instruments such as the Zeiss Jena Ni 002 and the establishment of a test network for leveling equipment at what is now the National Institute for Standards and Technology.

As of 2006, a Leica DNA03 is the standard leveling instrument used by NGS.

Program

Development of Official Elevation Datum

Geodetic computations are done with reference to a mathematical framework that is itself based on specific parameters and data – a datum. When necessary, data are combined and adjusted in order to remove observation and computation errors and to create a more accurate reference surface to serve as a datum. Datums are mathematically defined systems that provide internally consistent geodetic coordinates.

In the case of elevations, mean sea level as determined by tide gauges was used to create a vertical datum. The vertical datum is a mathematically defined surface to which heights refer and that has been determined using a collection of specific points on the Earth with known heights. This surface is often near, but not generally coincident with, mean sea level.

Round brass plates mark positions in the vertical datum. The markers are embedded in concrete or bedrock to maintain their positions and, therefore, the integrity of the geodetic control point. Click image for larger view and full caption.

The national network of elevation data (the “vertical network”) was added to rapidly and adjustments of the network were completed in 1900, 1903, 1907, and 1912. In 1929, Canadian leveling was added to the U.S. lines, and a total of 66,315 miles (106,724 kilometers) of leveling was adjusted. Known as the National Geodetic Vertical Datum of 1929 (NGVD 29), this vertical network was the official datum for elevations in the United States. NGVD 29 was the last adjustment of the data for nearly 60 years, and was used until the North American Vertical Datum of 1988 (NAVD 88) was released.

During the Great Depression, the federal government used emergency funds to hire unemployed workers to assist in the effort to expand the vertical network, allowing rapid completion of field work that would otherwise have taken years.

Re-leveling

Re-leveling revealed areas where benchmarks had been moved due to earthquakes, postglacial uplift, and subsidence due to the withdrawal of underground liquids such as water and oil. The post-World War II boom in highway construction led to the destruction of numerous benchmarks. Local adjustments of leveling data continued to be based on the NGVD 29, despite obvious problems in the network.

By the mid-1970s, about 388,360 miles (625,000 kilometers) of leveling had been added to the vertical network since the adjustment of NGVD 29. Thousands of benchmarks had been subsequently destroyed and the network had become distorted. Some distortions amounted to as much as 29.5 feet (nine meters) and were the result of forcing the new leveling data to fit NGVD 29 height values.

Realizing that accumulated distortions in the vertical network required a new adjustment, NGS began a multi-year re-leveling project in 1977. Disturbed and destroyed monuments were replaced, and stable, deep-rod benchmarks were set. Roughly 50,950 miles (82,000 kilometers) of re-leveling was needed.

In 1991, the result of the vertical adjustment of old and new leveling data, including Mexican and Canadian data, was released. This new datum, called the North American Vertical Datum of 1988 (NAVD 88), provides a more accurate vertical reference system for surveyors. A single tide mark at Father Point/Rimouski in Quebec was held fixed in the adjustment, thus also providing continuity for Great Lakes area elevations that are tied to the Father Point station and based on the International Great Lakes Datum of 1985 (IGLD 85).

Conclusion: GPS and Height Modernization

The global positioning system (GPS) has opened new horizons for mapping the surface of the Earth. Increased vulnerability of populations to flooding and other natural disasters has led to an increased need for accurate elevations.

The overall effort to modernize the vertical network in the United States is called “height modernization.” Height modernization provides accurate height information by integrating GPStechnology with existing survey techniques. NGS’s Height Modernization Program has combined classical spirit leveling with GPS to develop a method that enables vulnerable or rapidly changing areas to be mapped both quickly and accurately. The program also provides critical information for engineering, planning, and emergency management. While not as accurate as geodetic leveling alone, techniques used in the Height Modernization Program fill a critical need for vertical control in many areas of the nation.

For many of its 200 years, NOAA has led the way in mapping and modeling both the land and water of the United States. Now, in the 21st century, NOAA continues to pursue and produce the most accurate models of the Earth in order to meet the needs of an ever-shifting and growing population.

Contributed by Cindy Craig, NOAA’s National Ocean Service

Works Consulted

Berry, R.M. (1976). History of Geodetic Leveling in the United States. Surveying and Mapping, June 1976.

National Geodetic Survey. NGS FAQs. Retrieved September 1, 2006, from: http://www.ngs.noaa.gov/faq.shtml#WhatVD29VD88.

Smithsonian Virtual Surveying Instrument Collection. Levels. Retrieved September 21, 2006, from: http://americanhistory.si.edu/collections/surveying/type.cfm?
typeid=13.

Tittman, O.H. (1878). On Instruments and Methods Used for Precise Leveling in the Coast and Geodetic Survey. [Electronic Version]. Report of the Superintendent of the U.S. Coast and Geodetic Survey Showing the Progress of the Work during
the Year Ending with June 1879, 202-211.

U.S. Coast Survey. Report of the Superintendent of the Coast Survey Showing the Progress of the Survey during the Year 1857. p 352.

U.S. Department of Commerce, Coast and Geodetic Survey. (1931). First-Order Leveling. Serial 502. Washington, DC: U.S. Government Printing Office.

Whalen, C.T. (1978). Control Leveling. NOAA Technical Report NOS 73 NGS 8. Rockville, MD: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Survey.

Docket Number:
FDA-2014-D-0435
Issued by:

DRAFT GUIDANCE

This guidance document is being distributed for comment purposes only.
Document issued on: May 5, 2014

You should submit comments and suggestions regarding this draft document within 90 days of publication in the Federal Register of the notice announcing the availability of the draft guidance. Submit written comments to the Division of Dockets Management (HFA-305), Food and Drug Administration, 5630 Fishers Lane, rm. 1061, Rockville, MD 20852. Submit electronic comments to http://www.regulations.gov. Identify all comments with the docket number listed in the notice of availability that publishes in the Federal Register.

For questions regarding this document contact Robert J. Doyle at 301-796-5863 or via e-mail at robert.doyle@fda.hhs.gov.

U.S. Department of Health and Human Services
Food and Drug Administration
Center for Devices and Radiological Health
Office of In Vitro Diagnostics and Radiological Health
Division of Radiological Health
Magnetic Resonance and Electronic Products Branch

Preface

Additional Copies

Additional copies are available from the Internet. You may also send an e-mail request to CDRH-Guidance@fda.hhs.gov to receive a copy of the guidance. Please use the document number 1764 to identify the guidance you are requesting.

Surveying, Leveling, or Alignment Laser Products - Draft Guidance for Industry and Food and Drug Administration Staff

This draft guidance, when finalized, will represent the Food and Drug Administration's (FDA's) current thinking on this topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public. You can use an alternative approach if the approach satisfies the requirements of the applicable statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the appropriate number listed on the title page of this guidance.

Introduction

This draft guidance is intended for manufacturers of laser products and outlines the Food and Drug Administration’s (FDA’s or the Agency’s) proposed approach regarding the applicability of FDA’s performance standard regulations to surveying, leveling, or alignment (SLA) laser products.

The topics that are addressed include:

  • The definition of an SLA laser product
  • Examples of SLA laser products
  • Design features of SLA laser products
  • Applicability of class limits to SLA laser products
  • Questions and answers relating to the application of FDA’s performance standard regulations to SLA laser products

FDA's guidance documents, including this guidance, do not establish legally enforceable responsibilities. Instead, guidances describe the Agency's current thinking on a topic and should be viewed only as recommendations, unless specific regulatory or statutory requirements are cited. The use of the word should in Agency guidances means that something is suggested or recommended, but not required.

Surveying, Leveling, or Alignment (SLA) Laser Products

Leveling program surveying guide

Leveling Program Surveying Pdf

FDA regulates radiation-emitting electronic products, including all types of lasers. The Agency sets radiation safety product performance standards that must be met by manufacturers in order for laser products to be legally sold in the U.S. market. This draft guidance is intended to provide a brief summary of the FDA’s proposed approach on the applicability of FDA’s performance standards for laser products to specific purpose SLA laser products and is not a substitute for the performance standards themselves.

1. Question: What is an SLA laser?

Answer: SLA lasers are a subcategory of specific purpose laser products that transmit laser radiation through open space for surveying, alignment, or leveling purposes. An SLA laser is defined in 21 CFR 1040.10(b)(39) as 'a laser product manufactured, designed, intended or promoted for one or more of the following uses:

  1. (Determining and delineating the form, extent, or position of a point, body, or area by taking angular measurement.
  2. Positioning or adjusting parts in proper relation to one another.
  3. Defining a plane, level, elevation, or straight line.'

Leveling Program

It is important to note that a laser product can fall under the SLA laser definition even if it is not promoted for one of the three uses listed in the SLA laser definition or is explicitly promoted for a different use as long as the laser product is manufactured, designed, or intended for one or more of those SLA laser uses.

2. Question: What are some examples of SLA laser products?

Answer: Examples of products that FDA is aware of that are designed and manufactured for, if not also intended, or promoted for, one or more of the uses listed in 21 CFR 1040.10(b)(39), include but are not limited to:

  1. Laser pointers1
  2. Levels
  3. Tools incorporating laser guides
  4. Gun sights
  5. Target designators
  6. Night vision illuminators
  7. Visual disruptors

3. Question: What design features does CDRH consider specific to SLA lasers?

Answer: Certain design features allow SLA lasers to be used in open spaces or in unrestricted environments to determine and delineate the form, extent, or position of a point, body, or area by taking angular measurement, position or adjust parts in proper relation to one another, or define a plane, level, elevation, or straight line. These design features include:

Leveling Program Surveying Software

  1. Compact size (i.e. small, lightweight)
  2. Battery power
  3. Ergonomic design to permit hand-held use
  4. An aperture in the laser product's protective housing to transmit laser emission into open space
  5. Portability to permit use in open spaces or in unrestricted environments
  6. Features that utilize the laser’s straight line emission for surveying, leveling, or alignment

Generally, FDA will consider these design features as evidence that the laser product was designed for one or more of the uses listed in the SLA laser definition at 21 CFR 1040.10(b)(39). Therefore, FDA will generally consider laser products with these design features to fall under the definition of an SLA laser product and to be subject to the requirements identified in 21 CFR 1040.11(b) regardless of whether such laser products are promoted for SLA laser uses.

Design features that are not typical of an SLA laser include:

  1. Predictable, stable power input and output
  2. High quality power supply and/or power conditioning components
  3. Adjustability of power and wavelength
  4. Design that facilitates remote actuation2
  5. Non-portability
  6. Hard wire connection to power mains

4. Question: Why is a class limit imposed on SLA lasers?

Answer: The class limit in 21 CFR 1040.11(b) is intended to impose an upper exposure limit on accessible laser emission to ensure the safety of users and others. This limit takes into account the product’s intended uses and the generally unrestricted environments in which SLA laser products are used.

Note: 21 CFR 1040.11(b) establishes an upper class limit for all SLA laser products as Class IIIa, which has an accessible emission limit of 5 milliwatts.3 FDA has issued a proposed rule4 to amend the performance standards for laser products to achieve closer harmonization between the FDA’s current standards and the IEC standards. FDA has proposed that the IEC class limits be incorporated by reference into FDA’s regulations such that FDA’s class limits would be identical to the IEC class limits. Until this rule is finalized, FDA’s Center for Devices and Radiological Health (CDRH) does not intend to object to SLA laser emissions that are within the accessible emission limits for Classes 1, 2, and 3R in the International Electrotechnical Commission (IEC) International Standard 60825-1, “Safety of laser products- Part 1: Equipment classification and requirements,” Ed. 3.0 (IEC 60825-1) at Tables 3-7, since these are very similar to the class limits for SLA lasers in FDA’s regulations and adequately assure safety. However, because IEC Classes 1M and 2M do not have comparable analogs in FDA’s classification system, manufacturers should not conform to the parameters for IEC Classes 1M or 2M unless they also comply with FDA’s performance standards for laser products.

5. Question: May laser product manufacturers avoid the specific-purpose SLA designation simply by promoting the lasers for scientific, general-purpose, or other uses?

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Answer: No. As discussed above in the answer to Question 1, a laser product manufacturer may not avoid designation of its product as an SLA laser simply by promoting the laser product for non-SLA laser uses if the laser product is manufactured, designed, or intended for one or more of the uses listed in SLA laser definition. Therefore, promoting an SLA laser product for other purposes, such as science, treating pain, burning, security, or light reflection will not necessarily prevent the product from falling under the SLA laser definition. In determining whether a laser product was designed for one of the uses listed in the SLA laser definition, FDA looks at the design features identified in the answer to Question 3 above. The SLA designation imposes class limits on the accessible laser emission from laser products in order to promote their safe operation in generally unrestricted environments.

6. Question: When laser products have multiple purposes, which purpose will guide manufacturers in determining whether the laser product is an SLA laser?

Answer: When a laser product is manufactured, designed, intended or promoted for one of the uses listed in the definition of an SLA laser product at 21 CFR 1040.10(b)(39), the laser product will be subject to FDA’s performance standard applicable to SLA laser products even if the laser product also has non-SLA laser uses.

7. Question: Do other Federal agencies work with FDA to stop false or misleading promotions of regulated laser products?

Answer: Yes, FDA and the Federal Trade Commission work cooperatively to stop false or misleading promotions of FDA-regulated products.

1 Some laser pointers may be demonstration laser products, as defined in 21 CFR 1040.10(b)(13), if they are manufactured, designed, intended, or promoted for purposes of demonstration, entertainment, advertising display, or artistic composition. Laser pointers are subject to the same class limits regardless of whether they are classified as SLA laser products or demonstration laser products. See 21 CFR 1040.11(b) and (c).

2 See 38 FR 34084, 34085 (December 10, 1973).

3 This means that SLA lasers that emit invisible radiation (wavelengths up to and including 400 nanometers and wavelengths higher than 710 nanometers) may not exceed the accessible emission limits for Class I, because Classes IIa, II and IIIa do not include wavelengths outside the visible range.

4 78 FR 37723 (June 24, 2013).

Submit Comments

Leveling Program Surveying Guide

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