Azimuth Determination From Solar Observations

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Azimuth Determination FromSolar Observations

• ALAN M BERARDUCCI
• National Geomagnetism Program - US Geological
  Survey
• geomag.usgs.gov

2
Methods of Azimuth Determination

• Solar or Star Observations
• GPS
• Gyro compass

3
Equipment for Solar Observations

• Theodolite with
• Solar Filter
• Tripod or Pillar
• Watch or Clock
• Map or GPS

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Gurley Transit
5
Solar Filter
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Direct Azimuth determination
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Indirect Azimuth Determination
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Azimuth Monument
9
Preparation

• Synchronize clock to UTC.
• Obtain Lat and Long from GPS or Map.
• Set theodolite on tripod or pillar.
• Measurements made anytime except near noon.

10
Methodology

• Horizontal angles for azimuth and sun.
• Forward and reverse angles to Azimuth before and
  after sun readings.
• Equal number of forward and reverse readings to
  sun.
• Time accuracy to within 1 second.
• 2 to 8 sun readings on sun per set.
• 2 morning and 2 afternoon sets.

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Sun in Crosshair - Zeiss
12
Sun in Crosshair Right or Left edge
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Solar Observations Step 1-Sight the Azimuth Mark

• Place the vertical circle on the right with the
  telescope aimed at the azimuth mark.
• Precisely align the cross hairs with the azimuth
  mark.
• Record the horizontal circle reading on the
  observation form.
• Rotate the theodolite 180 so that the vertical
  circle is on the left with the telescope aimed at
  the azimuth mark.
• Precisely align the cross lines with the azimuth
  mark.
• Record the horizontal circle reading on the
  observation form.

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Solar ObservationsStep 2 Find sun in the
telescope

• Caution Never look at the sun through the
  telescope without a solar filter.
• Orient the horizontal circle so the telescope is
  facing the sun. Tip the objective end of the
  scope downward so that a shadow from the sun
  shows on the base of the theodolite.
• Do not look through the telescope during this
  procedure. Orient the shadow so that it is
  precisely centred on the theodolite base. Rotate
  the telescope upward until the bright light of
  the sun is visible through the telescope.
• Place the solar filter on the telescope. Look
  through the telescope and focus the sun so the
  edges are well defined. The Zeiss Jena
  theodolite has a circular hair which is a bit
  larger than the diameter of the sun.
• The idea is to move the telescope with the sun
  until it precisely aligned in the circular hair.
  At that moment, you stop moving the telescope and
  get the precise UTC time.

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Solar ObservationsStep 3 Direct Vertical
Circle Left

• With the vertical circle on the left, find the
  sun as described in Step 2 above.
• Align the sun in the circular hair. At the
  moment it is aligned, note the time and record it
  on the observation form.
• Record the horizontal circle reading on the
  observation form.
• Make three more observations on the sun with the
  vertical circle left. Record the time and
  horizontal angle on the observation form.

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Solar ObservationsStep 4 Reverse Vertical
circle right

• Remove the solar filter and eyepiece, rotate the
  theodolite 180 so that the vertical circle is on
  the right and find the sun as described in Step 2
  above.
• Align the sun in the circular hair. At the
  moment it is aligned, note the time and record it
  on the observation form.
• Make three more observations on the sun with the
  vertical circle right and record the time and
  horizontal angle on the observation form.

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Solar ObservationsStep 5 Sight on the azimuth
mark

• Place the vertical circle on the right with the
  telescope aimed at the azimuth mark.
• Precisely align the cross hairs with the azimuth
  mark.
• Record the horizontal circle reading on the
  observation form.
• Rotate the theodolite 180 so that the vertical
  circle is on the left with the telescope aimed at
  the azimuth mark.
• Precisely align the cross lines with the azimuth
  mark.
• Record the horizontal circle reading on the
  observation form.

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Computation of the Azimuth

• The simplest computation method is to use a
  computer program.
• Elgin, Knowles and Senne, Inc. has several
  products for comuter or HP 48 calculator
  http//www.rollanet.org/eksi/
• A freeware program is available from
• http//www3.sympatico.ca/craymer/spade/

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Computation (cont.)

• The procedure and formulas are also described in
  the Sokkia Celestial Observation handbook and
  Ephemeris, which is printed yearly.
• A Naval Almanac is available from
  http//aa.usno.navy.mil/publications/docs/ord_info
  .php

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Azimuth Determination From Solar Observations

• ALAN M BERARDUCCI
• National Geomagnetism Program
• US Geological Survey
• geomag.usgs.gov