(HP-65) Field Computation of Winds-Aloft Velocities

[SlideRule]

An extract from the six page article FIELD COMPUTATION OF WINDS-ALOFT VELOCITIES, USDA Forest Service Research Note PSW-320 (1976), Bill C. Ryan.

The ability to determine wind speeds and directions in the first few thousand meters of the atmosphere is important in many forestry operations such as smoke management, aircraft seeding and spraying, prescribed burning, and wildfire suppression. A hand-held electronic calculator can be used to compute winds aloft as balloon observations are taken. Calculations can be made in the field with any calculator with trigonometric functions, programmable or non programmable, by the method described.

The programmable calculator routine requires only the entry of the time interval in seconds between observations, balloon height in meters, and elevation and azimuth angles. In the following sections, this routine is first described through an example, as used with or without the rectangular-to polar-coordinate transformation function available on the HP-65. Then a brief summary of the steps is given, with program user instructions and a program list adaptable to the simplest calculator with trigonometric functions.

BEST!
SlideRule

[Thomas Klemm]

Quote:If the calculator's rectangular- to polar-coordinate transformation function is used, the azimuth angle \(A_t\), the angle of the balloon's position clockwise from north, must be transformed to angle \(a_t\) compatible with the calculator's axis orientation, in which 0° is to the east and angles increase counterclockwise.
This is accomplished by the transformation

\(a_t=90-A_t\)

This transformation is not really necessary. We just have to add 180° to the result:

Code:

01:    14 06        TAN
02:       71        ÷
03:    14 09        →R
04:    24 01        RCL 1
05:       41        -
06: 23 51 01        STO+ 1
07:       21        x<>y
08:    24 02        RCL 2
09:       41        -
10: 23 51 02        STO+ 2
11:       21        x<>y
12:    15 09        →P
13:    24 00        RCL 0
14:       71        ÷
15:       21        x<>y
16:       01        1
17:       32        CHS
18:    15 05        ACOS
19:       51        +

Initialisation:

60
STO 0
0
STO 1
STO 2


Example:

88.5 ENTER 216 ENTER 37.3 R/S
268.50
x<>y
4.73

78.1 ENTER 414 ENTER 45.8 R/S
235.62
x<>y
2.23

64.3 ENTER 612 ENTER 51.3 R/S
200.27
x<>y
2.30

55.8 ENTER 801 ENTER 52.3 R/S
207.42
x<>y
2.54

…

Cheers
Thomas