1. Pilot Balloon Radiosonde Upper Air Measurements

2. Pilot Balloon: Pibal A pilot balloon can be tracked visually with a single theodolite that measures the azimuth, relative to True North, and the elevation angle. If the balloon ascent rate is known (assumed from balloon and gas specifications), position of the balloon can be determined and the wind velocity inferred from successive balloon positions. The procedure is to track the balloon optically with the theodolite and measure the azimuth and elevation angles at 1 min or 30 s intervals. Height, z, is determined from the known or assumed ascent rate.

3. Z S Φ θ ElevationAzimuth X Y Pilot Balloon: Single Theodolite Geometry z = R sin Φ s = R cos Φ Solve for x and y: X = z cot Φ sin θ Y = z cot Φ cos θ X and y define the horizontal position of the balloon relative to the theodolite, S is the ground range to balloon, R is slant range to the balloon (R and S are your author's naming convetions) Side ViewTop ViewSide View θ R S x = S sin θ y = S cos θ

4. Pilot Balloon: Single Theodolite Geometry u = (x n -x n-1 )/(30 secs) v = (y n -y n-1 )/(30 secs) For 30 s intervals Horizontal wind speed = (u 2 +v 2 ) 1/2 Wind direction is computed following Appendix E. x, & y are in meters. u, & v are in meters/secs.

5. Calculate the wind profiles from the theodolite lab. Each student needs to digitize their lab book data and input the data into either Excel or a text file. A Pibal Spreadsheet will be on the class website. Once the profiles are calculated: Plot the profiles in two plots: 1. wind speed vs. z 2. wind direction vs. z Comment on the wind structure.

6. U and V to Wind Direction θ u v Top View WS u = -WS sin θ v = -WS cos θ WindDir = atan(u/v) with quadrant corrections θ is the geographic angle of the wind. WinDir is geographic but it needs quadrant corrections: From: http://www.wrh.noaa.gov/sew/fire/olm/transport.htm θ in this block is the quadrant correction

7. Double Theodolite Sometimes you do not know the exact inflation Of the balloon, so you can not calculate its ascent rate. You may also want to underinflate a balloon so that you get a more detailed view of the boundary Layer In these cases you can find the elevation of the balloon using 2 theodolites. You must know the distance between them and their azimuth angle of the other theodolite.

9. Radiosonde vs Piball What are the advantages of a radiosonde? Radiosonde returns: Position: Needs 2 GPS's Rh Tdp Temperature Pressure is often derived from Hydrostatic Equation Pibal Returns only wind speed and wind direction But Requires no electronics