M. Schoder 9.21.04
BLM CADASTRAL SURVEY HISTORY IN ALASKA – Part 1
THE START THROUGH AIRBORNE CONTROL ERA
This text is based primarily on the writing of Willard “Mike” Olson, PLS about his own Alaska BLM Cadastral Survey historical accounts. With permission from Mr. Olson (Oly) I have done some expounding on his text, and some minor editing. You can find Oly’s website at: http://home.gci.net/~wmocet
This is the first Part of a series of postings to describe the some of the activities and technologies that the BLM Cadastral Survey has used during the period of time from Statehood (1959) until modern day. As Forum Cadastral Survey Topic Moderator I would be glad to try to answer questions that might arise about these historical activities as I have a fair amount of insight to this topic matter and also have direct access to many others who were involved in these surveys.
– Michael Schoder, PLS
From the early days of Alaska Statehood to today, BLM-Cadastral Survey has been very active in delineating the boundaries of the Public Domain in Alaska. At the same time, there has been a continual searching and developing of the latest and most sophisticated survey technology in the world to assist this effort.
Surveying a state that was twice the size of Texas, consisting of 365 million acres of rugged terrain that was mostly road-less and uninhabited with a climate known for its severity and unpredictability, is perhaps the most challenging and difficult survey assignment undertaken in this past century, and it continues today some 45 years after Statehood. The BLM Cadastral Survey set out to develop the survey capabilities adequate to meet this challenge. BLM Cadastral Survey Alaska has been a forerunner in many applications of developing technologies to assist in the survey of Public Lands in Alaska.
One of the first steps undertaken by BLM was to protract a rectangular survey grid across the state. Establishing this grid overlay involved mathematically calculating the geographic position of every township and section corner within the state. A geographic position defines the latitude and longitude of any given point on the earth’s surface. Since there was only one datum at the time, NAD27, all geodetic positions for the protraction diagrams were referenced to this. Even in today’s age, surveys are referenced to NAD27 to maintain consistency and relationship to the PLSS protraction grid. NGS, then USC&GS assisted BLM in precisely locating all of the Alaska Initial Points to the NGS control network to form the accurate inter-relationships of the Initial Points. See C. Albert Whites “Initial Points” book for more details about the IP establishment.
The protracted grid of PLSS corner geographic positions would allow the surveyor to establish the position for all township and internal section corners independent of other township corners, without “building” one township upon another one as had previously been the only method used. Instead, the surveyor could orient original surveys to the sparse, yet available, state-wide Federal control network and layout the township corner locations by geographic positions using geodetic survey techniques. The geographic positions were published on “protraction diagrams” and have served as the basis for all Cadastral Surveys in Alaska since statehood. About this same time (early 1960s) highly accurate electronic instruments capable of measuring long distances were introduced and dramatically changed the method of surveying. Until this time distances had to be measured by some type chain or tape. Not only was this time consuming and very difficult in all areas, it was at times extremely difficult when it was necessary to cross rivers, canyons, etc. In those instances, it was necessary to calculate the distance by triangulation. With the application of the Electronic Distance Measurement (EDM) instruments it was possible to quickly and accurately measure distances between mountain tops, across rivers and canyons, and over the tops of trees and other thick vegetation that would have taken hours and days to have measured in the old conventional way. These early day era EDM’s had a range of 30 to 40 miles depending on the type terrain and ground cover between the two instruments.
In the late 50’s and early 60’s, the early days of statehood, BLM purchased two types of E.D.M. equipment. These were the Tellurometer and Hydrodist. The Tellurometer consisted to two units, one “master” unit and one “slave” designations. The master and remote units were set up on opposite ends of the survey line to be measured. The units were heavy and bulky and used car batteries for a power source. By today’s standards they were very crude and cumbersome but in the early 1960’s they represented state of the art technology. Distances of up to 50 miles could be measured, and because they were microwave based, line-of-sight was not needed.
Establishing primary control though out a project was accomplished by measuring the angles with a theodolite (modern transit) and the distance with the E.D.M. along traverse lines between existing geodetic control stations. Usually always a densification of the existing NGS control network in a project area was required.
The first real use of a “non-conventional” township survey included use of some for the time innovative procedures and the Tellurometer. For these surveys a survey crew which was normally transported to the site by helicopters would position themselves at a temporary point as near to a protracted corner location as possible, maintaining line-of-sight with the crew or crews located on one or more of these geodetic control stations. The position of the “roving crew” would then be established by measuring angles and distances (with the Tellurometer) from the known point. After the geographic position for the temporary point was calculated, a crew would then determine and monument the actual point for the corner (taken from the protraction diagrams) by a more conventional method of survey, (usually transit and tape).
The MRB-2 Hydrodist system was used in Alaska from 1963 through 1966. It consisted of two master units that would occupy existing geodetic control stations. A remote unit was carried in a helicopter which would hover over a point flagged on the ground as near to the predetermined location of the corner as possible. The distances to each of the master units were measured while the helicopter hovered over the flagged point on the ground. At the same time the measurements were being taken, surveyors at the master control stations would be measuring angles to the helicopter. The angle and distance measurements would require the helicopter to hover in the same position for approximately six to eight minutes. This method of survey was called the Airborne Control Survey System or more commonly simply “ABC” surveys.
After the position for the hovered and flagged point was calculated, a monument crew would return to the point and traverse from this point to the actual location of the corner and set the monument in the ground. Although this was basically the same method as using the Tellurometer previously described, it has the distinct advantage of allowing the “roving” surveyor to get nearer, and sometimes directly over, the corner point. This was possible because if the point chosen was not inter-visible with the control station, which was necessary with the first method, the surveyor could simply instruct the pilot to hover higher above the ground until line-of-sight contact was made. Hover heights of 50 to 100 feet above the ground were not uncommon.
A hover-sight mounted on the helicopter allowed the pilot to know when he was over the desired point while measurements were being taken. This was difficult at times and quite dangerous because of changing wind patterns, the strain this put the helicopter under, and because of the very rugged terrain where many of the corners were located.
The ABC method of survey required approximately seven surveyors, a geodist, camp cook, a helicopter pilot and mechanic. The Hydrodist system cost about $50,000 and the production rate averaged about three corners set per work day (six days per week). During the 1966 field season, because the area being surveyed was heavily timbered, four smoke jumpers were assigned to the crew. These smoke jumpers would parachute into an area and clear out the location where the corner was to be set. This would allow the helicopter to land so the survey crew could set the corner.
In July 1962 the first Alaska ABC Survey was performed by Fredrick W. Ward & Wallace E. Smith under Group No. 130. The platting and field notes also required diversions from the normal on the ground type of surveys, which is a different topic for discussion in itself. The plats and survey was approved on 6/20/1966. Once proven to work, and be productive, BLM really entered the age of “miles and monuments” where big production of original survey of the “Skelotonized” townships could commence. These type of surveys required original survey of Townships where the exterior boundaries were surveyed only, with a 2-mile monumentation interval as called for the the Alaska Statehood Selcetion MOU with the State, and later by Alaska Land Claims Settlement Act language.
BLM Cadastral Survey replaced the MRB-2 Hydrodist in 1966 with the cubic Dm-40 Auto-tape. This system as an automatic, electronic distance measuring system composed of an interrogator unit and three control station responder units. The operator in the hovering helicopter was able to measure distances to two units at the same time. With three units scattered on different control stations, it allowed for better checks and more flexibility, and made it possible to enlarge the work area so that more work could be accomplished before having to move crews to new control stations.
In 1972, BLM Cadastral Survey purchased the first four range system allowing the capability of Trilateration solutions in addition to the angular-distance solutions, or a combination of both. Trilateration is a method of computing positions using only the length of lines of the triangles, while triangulation incorporates both angles and lengths to compute the unknown position. This was the first airborne system to incorporate a magnetic tape unit to recover data. The tapes were input into a computer and teletype style printout was produced. The cost of the full-blown system was approximately $200,000.
This system required an operator in the helicopter and eight personnel on the four control stations. Depending on the terrain, an average of 20 corner positions could be established during the work day. On days when the weather was down, the eight people were used for corner setting. On an average, 1.5 million acres, or approximately 65 townships, were being field surveyed per Field Camp per year. This was a field production increase of over 500% compared to the first ABC methods.
For all practical purposes, this generation of survey technology gave way to the Inertial Survey System in 1975, although the ABC system was used to some extent until 1979.
Part 2 of this series will describe the AutoSurveyor age.
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