William H Crandall & Associates
Consulting Engineers
PO Box 36
Moncton, NB
February 23, 1960
SECRET
Chief of Air Staff
Air Force Headquarters
Ottawa, Ontario
Attention: CCE Victoria Island
Subject: Modification to True Azimuth, Maritime Gap Filler Sites
Dear Sir:
The survey requirements for True Meridian on the Maritime Gap Filler Sites call for an accuracy of plus or minus 5 secnds. This firm only occasionally has called for True Meridan to this accuracy and in the past each requirement has been separately without recourse to a formal tabular form.
Because of the number of calculations involved in the Gap Filler Sites a tabular form was drawn up which incorporated a different procedure then normally used by the field crews heretofore. In carrying out the calculations on the Gap Filler Sites a very annoying progression in the values occurred. We knew this error was due to either a transposition of position or an error in our Hour Angle. We have just discovered the cause of the error which involved the inclusion of the same correction twice giving us an incorrect time of site. We have recalculated all six sites and forward to you the attached calculations.
All sites with the exception of New Yarmouth were determined by a DKM-3. New Yarmouth was determined by the use of a DKM-2 which is a second order instrument. Since some of the sites are excellent and others are not quite the first order accuracy I feel that a word of explanation on each station is in order.
Since New Yarmouth is the only station done with a DKM-2 I will comment on it first. The first four sets of shots are nicely grouped with a spread of 3.2 seconds. The second set is not badly grouped either with a maximum spread of 5.7 seconds. The difference between the first and second group of approximately 10 seconds is probably due to a slight settlement of the instrument or else it was knocked or jarred slightly. Because the first group was probably based on a more accurate setting we have chosen to neglect the second group altogether and have given you an average on the first four sets.
Each set of shots is based on six sitings which have been averaged out so that a set of four actually represents twenty-four individual sitings on the star. We feel this is quite sufficient for the order of accuracy you are requesting.
Six sets are included on Mount Carleton. Weather conditions at this site were extremely bad and two attempts were made before a satisfactory series of shots were obtained. Two geodetic monuments were visable from the top of Mount Carleton and since the check on these indicated an angular error not exceeding the allowable tolerance these shots were accepted to spite a spread above normal.
Les Etroits again was plagued by bad weather. The two sets involving 12 shots, however, was close enough that the result we feel was quite acceptable. If desired this bearing could be checked at a later date when the land survey work on site is carried on.
The St Joseph site had a nice grouping of four and one which was off approximately 15 seconds which we rejected. I would consider this set a perfectly normal one with a spread of about 5 seconds. A stride level was used on all of these sites but Todd Mountain and Mount Carleton but no correction was made for the variations in the stride level. This correction might probably refine your results upwards of a second or more.
Alder River is a very similar situation to St Josephs. A nice grouping of three sets with one reject. This set points out a particular difficulty with the short distances between monuments. It would appear that the instrument was not firmly settled in the ground for set No 1 or else at the completion of set No 1 the instrument was jarred slightly. A lateral displacement of either the instrument or the plumb bob centered over your back site of a distance not exceeding 1/16 of an inch in either case would give an error of five seconds in the 300 foot back site. Alder River was the only set on which corrections for the stride level were considered. it is interesting to note that the grouping of the three range only over .5 seconds of Arc.
Todd Mountain consists of 20 shots taken over two nights. This procedure was decided upon after the progression became apparent in the first set of calculations on New Yarmouth. Twelve of the 20 shots followed in the 5 second grouping approximately which is more than adequate for the determination of Azimuth on this site. As a result of these calculations, however, it was determined to purchase a stride level for the DKM-3 and while we have not had an opportunity as yet to have the National Research Council calibrate this level it would appear from the Alder River grouping that there is very little error in it.
As I mention earlier this is the first opportunity this firm has had to carry out a series of these shots in sufficient number to draw any conclusions as to field procedure and probable ultimate accuracy. From the results on these six sites we are now of the opinion that 2 second accuracy could be achieved during one night's operation and probably this could be refined to 1 second accuracy or better over a two night sequence. To achieve this we feel that a concrete base would have to be provided for the instrument or that three iron posts be driven solidly into the ground to support each leg of the tripod. In addition the backsite on monuments should be a minimum distance of 2000 feet apart. While accuracies of this order have no particular use or significance as far as True Meridan is concerned it does present a possible means of establishing your true geographical position to within 1 second of Arc probably error and within 2 seconds of Arc maximum error. I have no knowledge as of significance of the accuracy of your geodetic or geographical position in connection with these sites but if further field work is involved in any of these sites we would like the opportunity of checking one of them by this method to determine costg, field procedures and probable accuracy. It would be most advisable if the position so determined could be checked by the three point method from existing triangulation stations.
This has been a rather lengthy letter to advise you of the correction on six bearings but I thought the background work and our conclusions might be of some assistance to you at a future date.
Sincerely yours,
W H CRANDALL & ASSOCIATES
W H Crandall, P Eng