VK3UM Atmosphere Attenuation Calculator. Table of Contents

Transcription

1 Table of Contents Over View 2 Menu Options 2 Input Variables 5 Input application data. 7 Screen Display Calculations 11 Reference ITU Graphs 13 Terrestrial Dry Air [O²] and W V [H²O] Attenuation 14 Zenith Dry Air [O²] and W V [H²O] Attenuation 16 Rain Attenuation 18 Slant Paths 19 Acknowledgement 21 References 22 Author 23 Page 1

2 Atmosphere Absorption Attenuation [Attenuation by atmospheric Gasses] Electromagnetic waves are absorbed in the atmosphere according to wavelength. Two compounds are responsible for the majority of signal absorption, Oxygen (O ² ) and water vapor (H ² O). The first peak occurs at 22 GHz due to water vapor, and the second at 63 GHz due to oxygen. The actual amount of water vapour and Oxygen in the atm osphere normally declines with an increase in altitude because of the decrease in pressure. Total attenuation through the atmosphere at any frequency, through unobstructed atmosphere, is the sum of free space path loss, attenuation caused by oxygen absorption, and attenuation caused by water vapour absorption. Rain attenuation, when present adds an additional element. Total path attenuation = Attenuation Free Space Path Loss + Attenuation caused by Oxygen + Attenuation due to Water vapour + Attenuation due to Rain. This program [Atmosphere] calculates the absorption attenuation at Microwave frequencies for both terrestrial and slant paths for Amateur frequencies from GHz. The calculations applied in this program are based upon the International Telecommunication Union (ITU) recommended methods as listed in the Referenc e section of this Document. The program has been written primly as a supplement to my EME Calculator Program to refine overall loss calculations for frequencies above 10 GHz where these factors become a significant. refer.. The EMECalc program available for download from This program has been designed to be best viewed under Windows XP Style. This can be set from the Desk Top by Properties/Display Properties/ Appearance and then choose Windows XP Style. Menu Options Save default Data All the parameters that appear on the sc reen will be saved and will be used when the program is run again. The following message will be displayed on its completion. Page 2

3 Change Display Accuracy The calculation displayed accuracy may be changed as desired by clicking on the required decimal points. The display below indicates 3 decimal digits will be displayed. On Screen Help Display This allows for the time the on screen help messages (yellow) are displayed. Reset Screen Size Resets the Screen size to the default dimensions. Cloud yearly % location maps Select the Cloud Columnar content map that is appropriate to your loc ation. Then adjust the slider commensurate with you location. Page 3

4 Help Displays this Help File About Provides the Build version and date of the software. Exit Soft Exit from this program Version The software version of this software. Page 4

5 Input Variables Temperature in c. Pressure in hpa. Frequency in GHz. Humidity in %. Distance in kms [for Terrestrial calculations]. Elevation in degrees [for Slant Attenuation]. Rain precipitation rates in mm/h [for both terrestrial and Slant attenuation c alculations]. Selectable Polarisation [horizontal, vertical, circular]. Calculations provided. Terrestrial Dry Air Attenuation in db per kilometres at Sea Level. Water Vapour attenuation in db per kilometres at Sea Level. Total attenuation of Dry Air and Water Vapour in db per kilometres at Sea Level. Total combined attenuation over a path length per kilometres as input by the user Rain Attenuation for horizontal, vertical or circular polarisations at various rain precipitation rates. Path Aperture Loss. Page 5

6 Slant Attenuation for both (independent) Home and Dx Stations Dry Air Attenuation in db per kilometres at Sea Level. Water Vapour attenuation in db per kilometres at Sea Level. Dry Air height in kilometres. [refer Rec. ITU-R P.676-7] Wet Vapour height in kilometres. [refer Rec. ITU-R P.676-7] Dry Air attenuation at height in db at zenith. Water Vapour attenuation at height in db at zenith. Total Attenuation (Dry Air + Water Vapour) at zenith. Total Attenuation (Dry Air + Water Vapour) at user selected Elevation angle. (5-90 ) Rain Attenuation for horizontal, vertical or circular polarisations at various rain precipitation rates. Fog Attenuation at various fog distance visibility distanc es. Cloud Attenuation at a specific Cloud Columnar content. Added attenuation to Earth Moon Earth (EME) path. Page 6

7 Input application data. The following input variables may be changed to suit your application. Use the Up/Down arrows to change the parameter as required. Temperature : Humidity : Pressure The combination of the humidity and the temperature will give the water vapour density in grams per cubic centimeter. By clicking on the Water vapour Density label you can change to Ice Vapour Density. Frequency Selectable for all Amateur Bands from 10 GHz to 241 GHz. The 100 GHz option is provided to check measurements against known values. Note. Although the frequencies of 10, 24 and 47 GHz are shown in the display the ac tual frequencies used in the program are , and GHz. Rain and Polarisation (Relevant to Rain attenuation.) Cloud Columnar Content. Click on this button to select the Average Year % Liquid Water m aps. which will reveal this panel Page 7

8 Choose the Cloud yearly % map applicable to your location and time of year. Note the value and adjust the Cloud Columnar Slider to this value. The value of Cloud attenuation will be provides as well as the specific H²O attenuation coefficient. Height above Sea Level. This option is currently not incorporated in the program overall end calculations. It provides the temperature (in centigrade and Kelvin), pressure (in hpa) and water vapour content (in g/cm³) commensurate with the reference standard atmosphere at selectable heights above sea level (HASL) adjustable by the arrow keys. First click on the Ref Latitude and season button to reveal the Reference Latitude Panel. Choose the Latitude applicable to your location and the season applicable to your time of year. Note that the Season selection only applies to latitudes greater than ± 22 from the equator. The data will be computed as shown in the following panel. Reference ITU Recommendation P Standard Temperature k Standard pressure hpa Calculations as per pages 4-6 (inc) Distance Page 8

9 Adjust for Terrestrial applications. The 3 adjustment arrows provide for x100, x10 and x1 variations. The Free Space Path Loss is calculated from the Distance and frequency selected. Elevation Adjust for the angle of the slope path for Space applications [eg EME] through the atmosphere. Default is Zenith [90 ] and variable down to 5 degrees. Additional Features. Save Default Data. Click on this to save your set up that will load at start of the program. On Screen Display Accuracy It should be noted however that the maximum accuracy of the calculated values is approximately 10% and to utilise the higher resolution provided is not an indic ation of increased accuracy. This value may be saved as part of you default start up values. On Screen Help Delay This option provides the selection of the time that the on screen help display shows the message under the cursor (where provided). It may be varied from off (no message displayed to a maximum of 8 seconds). This value may be saved as part of you default start up values. Help.. About.. Exit.. Version Help provides this help information. Page 9

10 About Provides the Author details, Build number and Date. Exit Provides a safe Exit from the program. Version The on screen version number of the Program release. Page 10

11 Screen Display Calculations Calculations Terrestrial Attenuation Free Space Path Loss (aperture Loss) for the path distance selected Dry Air Attenuation (O ² ) in db per kilometres at Sea Level. Water Vapour attenuation (H ² O) in db per kilometres at Sea Level. Total attenuation of Dry Air and Water Vapour in db per kilometres (as selected by the user) at Sea Level. Total combined attenuation [O + H O] over the path length as chosen by the user. ² ² Rain Attenuation for either horizontal, vertical or circular polarisations as selected.. Slant Attenuation (for both Home and Dx Stations) Page 11

12 Dry Air Attenuation (O ² ) in db per kilometres at Sea Level. Water Vapour attenuation (H ² O) in db per kilometres at Sea Level. Dry Air (O ² ) equivalent height in kilometres. Wet Vapour (H ² O) equivalent height in kilometres. Dry Air attenuation (O ² ) at equivalent height in db at zenith. Water Vapour attenuation (H ² O) at equivalent height in db at zenith. Total Attenuation (Dry Air + Water Vapour) at zenith. Total Attenuation (Dry Air + Water Vapour) at user selected Elevation angle. (5-90 ) Rain Attenuation for either horizontal, vertical or circular polarisations as selected. Fog Attenuation. Cloud Attenuation. Additional attenuation added to Earth Moon Earth (EME) path, and the Home and Dx Station added combined losses. The Home and Dx Station Total additional Loss values are those to be inserted into the VK3UM EMECalc program which will then provide the additional accuracy of calculations for frequencies above (including) 10 GHz Current Moon Distance When the program is started the current Moon distance, path loss and phase values are calculated. The current Moon distance will be shown as above and the slider will show its position. The slider may be varied as required (from Perigee to Apogee) and may also can be reset to the current (local computer time) Moon Distance. Page 12

13 Reference ITU Graphs The included graphs provide a means of checking the programs calculated values to those of the ITU recommended calculation procedure. It should be noted that the computed figures may [in some cases], be within 10% of the theoretical values due to the nature of the applicable formulae commensurate with the c urve form fit procedures used. Page 13

14 Terrestrial Dry Air [O ² ] and Water Vapour [H ² O] Attenuation This graph is from ITU RECOMMENDATION ITU-R P.676-7, "Attenuation by atmospheric gases." [Page 16] The graph provides the attenuation values at terrestrial paths for both Dry Air, Water Vapour and the combined total for an Atmospheric pressure of 1013 hpa, a temperature of 15 c and a water vapour c ontent of 7.5 g/cm³. Page 14

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16 Zenith Dry Air [O ² ] and Water Vapour [H ² O] Attenuation This graph is from ITU RECOMMENDATION ITU-R P.676-7, "Attenuation by atmospheric gases." [Page 19] The graph provides the attenuation values at zenith for both Dry Air, Water Vapour and the combined total for an Atmospheric pressure of 1013 hpa, a temperature of 15 c and a water vapour c ontent of 7.5 g/cm³. Page 16

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18 Rain Attenuation This graph is an extract from the "PROPOSED REVISION TO RECOMMENDATION ITU-R P.838". [page 13] The proposed changes have been applied in this program. -o- Page 18

19 Slant Paths Page 19

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21 Acknowledgement I wish to acknowledge the considerable help from John Drew VK5DJ in converting many of the complex mathematical expressions into the Pascal language, and also Dr Mike Willis G0MJW for his assistance in obtaining the latest ITU Recommendations (as a member of the Study Group directly involved) as well as his valued suggestions and help with some of the complex calculation scripts. Page 21

22 References International Telecommunication Union Publications ITU-R P Attenuation by Atmospheric Gases. ITU-R P Attenuation Due to Clouds and Fog. ITU-R P Propagation data and prediction methods required for the design of Earth-space telecommunication systems ITU-R P Specific attenuation model for rain for use in prediction methods. ITU-R P Water vapour: surface density and total columnar content. ITU-R P The Radio Reflective Index : its formula and reflectivity data. Page 22

23 Author This program has been written by Doug McArthur [VK3UM]. Web Site Contact... tikaluna at bigpond.com First draft concept release July First Beta restricted release September 2011 Program written with the Delphi 2007 platform in the Pascal language. Page 23

24 Index GHz option 7 - A - About 13 Additional attenuation 11 Additional Features 7 Amateur Bands 7 Apature Loss 11 Atmosphere Absorption Attenuation 2 Attenuation by Atmospheric Gases. 22 Attenuation Due to Clouds and Fog C - Change Display Accuracy 13 Cloud Attenuation 11 Cloud Columnar Content 7 Cloud Columnar Slider 7 Cloud yearly % location maps 13 Current Moon Distance 11 - D - design of Earth-space telecommunication systems 22 Distance 7 Doug McArthur 23 Dry Air Attenuation 11 - E - Electromagnetic waves 2 Elevation 7 EME Calculator Program 2 EMECalc 2 Exit 13 - F - Fog Attenuation 11 Free Space Path Loss 7, 11 Frequency 7 - H - Page 24

25 Height above Sea Level. 7 Help 13 Help.. About.. Exit.. Version 7 Home and Dx Station added combined losses 11 Home and Dx Station Total additional Loss 11 Humidity 7 - I - Ice Vapour Density 7 input variables 7, 5 International Telecommunication Union (ITU) 2 ITU-R P ITU-R P ITU-R P ITU-R P ITU-R P L - Lattitude 7 - M - maximum accuracy 7 Menu Options 2 - O - On Screen Display Accuracy 7 On Screen Help Delay 7 onscreen help display 7 Oxygen (O²) 2 - P - Polarisation 7 Pressure 7 - R - Rain 7 Rain Attenuation 11 Ref Lat and season 7 Reference Latitude Panel 7 Reset Screen Size 13 - S - Save default Data 13 Save Default Data. 7 season 7 Slant Attenuation 11 Slant Paths 19 Page 25

26 slope path 7 Space applications 7 Specific attenuation model for rain 22 specific H²O attenuation coefficient 7 - T - Temperature 7 Terrestrial Attenuation 11 The Radio Reflective Index 22 Total attenuation of Dry Air and Water Vapour 11 Total combined attenuation 11 - W - water vapor (H²O) 2 Water vapour 22 Water Vapour attenuation 11 water vapour density 7 - Z - Zenith [90 ] 7 - [ - [Attenuation by atmospheric Gasses Page 26