LOCAL WEATHER CONDITIONS EFFECTS ON DETECTION CAPABILITY OF SOUTH EASTERN AFRICAN INFRASOUND STATION

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Avice Dennis
5 years ago
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STATION RAMANANTSOA Andry Harifidy Institute and

1 LOCAL WEATHER CONDITIONS EFFECTS ON DETECTION CAPABILITY OF SOUTH EASTERN AFRICAN INFRASOUND STATION RAMANANTSOA Andry Harifidy Institute and Geophysical Observatory of Antananarivo Antananarivo University MADAGASCAR

2 INTRODUCTION Ø Detection decreases considerably during daytime 2

3 Ø When temperature or wind increases, background noise power increases and masks infrasound signal Ø In term of detection number, temperature controls mainly the diurnal variation and surface wind controls mainly the seasonal variation. Ø P(V)=a.exp(bV) Ø P(T)=c.exp(dT) at high frequency bands al low frequency band Ø For having low background noise, temperature should not exceed 15 C and surface wind speed not more than 1.5 m/s. 3

4 Purpose: Do local weather c o n d i t i o n s (temperature, wind speed) have effect on background noise or/and detection in other infrasound station (South Eastern Africa stations)? 4

5 DATA ACQUISITION AND METHODS q Data from 2009 to 2011 of I35NA and I47ZA are used. q Pressure data are filtered into 4 frequency bands centered respectively at 1 Hz, 0.25 Hz, Hz and Hz. q Temperature and surface wind speed are correlated with power of background noise in order to have exponential law in first step. q PMCC method is used for data processing 5

6 RESULTS AND DISCUSSION I35NA DIURNAL VARIATION 6

7 I35NA TEMPERATURE EFFECT: DIURNAL VARIATION r= r= r= r=

8 I35NA SURFACE WIND EFFECT: DIURNAL VARIATION r= r= r= r=

9 I35NA SEASONAL VARIATION DECEMBER JANUARY - FEBRUARY JUNE JULY - AUGUST 9

10 I35NA TEMPERATURE EFFECT: SEASONAL VARIATION r= r= r= r= r= r= r= r=

11 I35NA SURFACE WIND EFFECT: SEASONAL VARIATION December January - February June July - August r= r= r= r= r= r= r= r=

12 I35NA DIURNAL VARIATION Ø Temperature controls diurnal variadon Ø Temperature has effect at low frequency, mainly at Hz Ø Surface wind has effect mainly at high frequency SEASONAL VARIATION Ø Surface wind controls the seasonal variadon in all frequency band Ø Temperature variadons do not follow exponendal law except at low frequency band. 12

13 I47ZA DIURNAL VARIATION 13

14 I47ZA DIURNAL VARIATION TEMPERATURE EFFECT SURFACE WIND EFFECT r= r= r= r= r= r= r= r=

15 I47ZA SEASONAL VARIATION DECEMBER JANUARY - FEBRUARY JUNE JULY - AUGUST 15

16 I47ZA TEMPERATURE EFFECT: SEASONAL VARIATION DECEMBER JANUARY - FEBRUARY JUNE JULY - AUGUST

I47ZA SURFACE WIND EFFECT: SEASONAL VARIATION 0.

17 I47ZA SURFACE WIND EFFECT: SEASONAL VARIATION

18 I47ZA DIURNAL VARIATION Ø Effects of temperature and surface wind are felt in all frequency band. Ø Temperature effect at low frequency and effect of surface wind at high frequency are observed I47ZA SEASONAL VARIATION Ø Effects of temperature and surface wind have both effect in seasonal variation. Ø Temperature effect at low frequency and effect of surface wind at high frequency are observed. 18

19 COMPARISON OF I33MG, I35NA AND I47ZA I33MG I35NA I47ZA Shape Triangle Triangle Pentagone Element number Noise reducing filter Rose]e 18m 32elts Rose]e 18m 96elts Rose]e 36m 144elts Diurnal variadon Temperature effect important Temperature effect important No difference in Temperature and wind effects Seasonal variadon Surface wind effect important Surface wind effect important No difference in Temperature and wind effects 19

20 THANK YOU FOR YOUR ATTENTION 20

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