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Medium frequency radar observations in the middle atmosphere
Journal ofAtmo.~pheric und Terrestrial Ph)'sicx, Vol. 45, No. 10, pp. 729-732 1983. Printed in Great Britain.
0021-9169/83 $3.00 + .00 Pergamon Press Ltd.
Short Paper
MEDIUM FREQUENCYRADAROBSERVATIONS IN THE MIDDLE ATMOSPHERE
P. Czechowsky, G. Schmidt and H. Kopka
Max-Planck-lnstitut fur Aeronomie, 3411Katlenburg-Lindau, F.R.G.
(Received for publication |6 August 1983)
Abstract - In November 1982 the Heating and the PRE (Partial Reflection Experiment) f a c i l i t y near Troms~ (Norway) were operated together in a pulsed mode as a radar system to investigate structures in the middle atmosphere. For the f i r s t time echoes from the upper troposphere and stratosphere have been detected on a frequency of 2.75 F~z. Introduction The Max-Planck-lnstitut fur Aeronomie is planning a multifrequency experiment to investigate the structure and dynamics of the middle atmosphere in a wide frequency range. For this purpose a p i l o t experiment was carried out on 2.75 MHz during one week in Nov/Dec 1982 in order to optimize system parameters such as the pulse repetition period, the pulse length and the number of coherent integrations to increase the resolution and the sensit i v i t y of the radar. The s c i e n t i f i c objective of these measurements was the detection of scattering structures in the troposphere and stratosphere in parallel to the well known mesospheric layers (see e.g. Gregory and Vincent, 1970; Schlegel et a l . , 1978). Experimental set-up The radar used during this p i l o t experiment consisted of different components of the PRE f a c i l i t y (Holt et al., 1980), the Heating f a c i l i t y (Stubbe et a l . , 1982), and the SOUnding SYstem (SOUSY) {R~ttger et a l . , 1981). The operational frequency was 2.75 MHz. To detect turbulent scattering from tropospheric and stratospheric heights optimum operational and technical conditions are required such as a maximum power aperture product, a substantial
730
Short Paper
suppression of antenna side-lobes to prevent the influence of spurious signals and ground c l u t t e r , and a f l e x i b l e radar controller to modify the pulse repetition period PRP, the coding and the spectral resolution Af. The table summarizes the main operational parameters of the modules of the three systems: S~stem
Module
Parameter
PRE
Receiving antenna
Elements: 16 crossed dipoles Gain: 17 dB Half power beam width: 22~ *)
Heating
Transmitter
Peak power: 1.2 MW Duty cycle: max. 4%
Transmitting antenna
Elements: 36 crossed dipoles Gain: 23 dB o Half power beam width: 15
Receiver, Adder, Radarcontroller, Tape unit
PRP: 1 ms, 4~ms Af: 9.38.10"~Hz, 2.34.10-2Hz Height resolution ~h: 3 km
SOUSY
The advantage of using the PRE antenna for reception and the Heating antenna for transmission is based on the different size (16 and 36 crosseddipoles) and therefore on the different shape of the radiation patterns. The product of both antenna diagrams leads to a side lobe reduction of more than 25 dB since the sidelobe maxima of one antenna coincide with the minima of the other one. Therefore, the probability of receiving oblique radar echoes from the E- and F-region at low elevation angles is largely reduced. Results and discussion The measurements were carried out for one or two hours per day during the period from Nov 29 to Dec 2, 1982. The radar was operated with different pulse repetition periods (PRP) of 1 ms and 4 ms, partly applying the pulse coding technique (see e.g. Schmidt et a l . , 1979). Fig. i shows a representative result obtained on Nov 30 from 1025-1100 LT and from 12041220 LT. The 3-dimensional plot presents 67 power profiles observed in the altitude range from 15 to 102 km. In addition to the well known layers in the mesosphere s i g n i f i c a n t radar echoes were detected for the f i r s t time at stratospheric heights. The mean decay of the echo power with height below 35 km is about 2.1 dB/km which is comparable with results derived from radar measurements in the VHF range (RUster et al., 1980). The echo intensity and the vertical velocity were derived from the power spectra after eleminating the DC peak resulting from ground c l u t t e r . Spurious signals induced by E- and F-region reflection were attenuated by oversampling and coherent integration which acts as a combfilter. The remaining interference was removed by spectral f i l t e r i n g . As demonstrated in Fig. 2 multiple scattering or reflection from E-region heights between 110 km and 140 km (three signal traces are denoted as "1", "2" and "3") do cause interference with atmospheric echoes at subsequent gatings, but at different heights. Since 166 pulses were coherently added to form one burst i t seems evident that E- or F-region echoes w i l l cause only an enhancement of the background noise. There is no indication for *) D. Leiulfsrud, Auroral Obs. Troms~, private communication
732
Short Paper
E
PRP: 2.1856-1921 12.1ms 82LT
7S.
N
I 2.12.82LT ~801-1826 /,ms
30.
15-
0
Fig. 3.
I 20
I 40
P/dB w/rns-~ 60
-0.2
0
I 20
I /.,0
PIdB
I
60
J -O2
0
wlms-1
Mean power and velocity profi|es measured with PRP of 1 ms and 4 ms.
Conclusion Radar measurements have been carried out on 2.75 MHz near Troms~ (Norway) to investigate structures in the middle atmosphere in the medium-frequency band. The results indicate the occurrence of 50 m-irregularities in the stratosphere which were observed for the f i r s t time. Acknowledgements
-
The authors would like to thank the Auroral Observatory (Troms~/
Norway) for the permission to use the antenna of the PRE f a c i l i t y during this radar experiment. The i n i t i a l discussion about this experiment with J. R~ttger and the constructive comments from R. R~ster and J. K1ostermeyer are gratefully acknowledged. References R6ttger J., Czechowsky P. and Schmidt G.
1979
Preprints 17th Radar Meteor. Conf., 349
Greqory J.B. and Vincent R.A.
1970
J. geophys. Res. 7__55,6387
Holt 0., Brekke A. and Hansen T.
1980
Proc. Vth ESA-PAC Symposium, Bournemouth, 387
R~ster R., Czechowsky P. and Schmidt G.
1980
Geophys. Res. Lett. ~, 999
Schlegel K., Brekke A. and Haug A.
1978
J. atmos, terr. Phys. 40, 205
Schmidt G., RUster R. and Czechowsky P.
1979
IEEE Trans. Geosci. Electron. GE-17, 154
Stubbe P., Kopka H., Lauche H., Rietveld M.T., Brekke A., Holt 0., Jones T.B., Robinson T., Hedberg A., Thide B., Crochet M. and Lotz H.J.
1982
J. atmos, t e r r . Phys. 44, 1025
732
Short Paper
E
PRP: 2.1856-1921 12.1ms 82LT
7S.
N
I 2.12.82LT ~801-1826 /,ms
30.
15-
0
Fig. 3.
I 20
I 40
P/dB w/rns-~ 60
-0.2
0
I 20
I /.,0
PIdB
I
60
J -O2
0
wlms-1
Mean power and velocity profi|es measured with PRP of 1 ms and 4 ms.
Conclusion Radar measurements have been carried out on 2.75 MHz near Troms~ (Norway) to investigate structures in the middle atmosphere in the medium-frequency band. The results indicate the occurrence of 50 m-irregularities in the stratosphere which were observed for the f i r s t time. Acknowledgements
-
The authors would like to thank the Auroral Observatory (Troms~/
Norway) for the permission to use the antenna of the PRE f a c i l i t y during this radar experiment. The i n i t i a l discussion about this experiment with J. R~ttger and the constructive comments from R. R~ster and J. K1ostermeyer are gratefully acknowledged. References R6ttger J., Czechowsky P. and Schmidt G.
1979
Preprints 17th Radar Meteor. Conf., 349
Greqory J.B. and Vincent R.A.
1970
J. geophys. Res. 7__55,6387
Holt 0., Brekke A. and Hansen T.
1980
Proc. Vth ESA-PAC Symposium, Bournemouth, 387
R~ster R., Czechowsky P. and Schmidt G.
1980
Geophys. Res. Lett. ~, 999
Schlegel K., Brekke A. and Haug A.
1978
J. atmos, terr. Phys. 40, 205
Schmidt G., RUster R. and Czechowsky P.
1979
IEEE Trans. Geosci. Electron. GE-17, 154
Stubbe P., Kopka H., Lauche H., Rietveld M.T., Brekke A., Holt 0., Jones T.B., Robinson T., Hedberg A., Thide B., Crochet M. and Lotz H.J.
1982
J. atmos, t e r r . Phys. 44, 1025
0021-9169/83 $3.00 + .00 Pergamon Press Ltd.
Short Paper
MEDIUM FREQUENCYRADAROBSERVATIONS IN THE MIDDLE ATMOSPHERE
P. Czechowsky, G. Schmidt and H. Kopka
Max-Planck-lnstitut fur Aeronomie, 3411Katlenburg-Lindau, F.R.G.
(Received for publication |6 August 1983)
Abstract - In November 1982 the Heating and the PRE (Partial Reflection Experiment) f a c i l i t y near Troms~ (Norway) were operated together in a pulsed mode as a radar system to investigate structures in the middle atmosphere. For the f i r s t time echoes from the upper troposphere and stratosphere have been detected on a frequency of 2.75 F~z. Introduction The Max-Planck-lnstitut fur Aeronomie is planning a multifrequency experiment to investigate the structure and dynamics of the middle atmosphere in a wide frequency range. For this purpose a p i l o t experiment was carried out on 2.75 MHz during one week in Nov/Dec 1982 in order to optimize system parameters such as the pulse repetition period, the pulse length and the number of coherent integrations to increase the resolution and the sensit i v i t y of the radar. The s c i e n t i f i c objective of these measurements was the detection of scattering structures in the troposphere and stratosphere in parallel to the well known mesospheric layers (see e.g. Gregory and Vincent, 1970; Schlegel et a l . , 1978). Experimental set-up The radar used during this p i l o t experiment consisted of different components of the PRE f a c i l i t y (Holt et al., 1980), the Heating f a c i l i t y (Stubbe et a l . , 1982), and the SOUnding SYstem (SOUSY) {R~ttger et a l . , 1981). The operational frequency was 2.75 MHz. To detect turbulent scattering from tropospheric and stratospheric heights optimum operational and technical conditions are required such as a maximum power aperture product, a substantial
730
Short Paper
suppression of antenna side-lobes to prevent the influence of spurious signals and ground c l u t t e r , and a f l e x i b l e radar controller to modify the pulse repetition period PRP, the coding and the spectral resolution Af. The table summarizes the main operational parameters of the modules of the three systems: S~stem
Module
Parameter
PRE
Receiving antenna
Elements: 16 crossed dipoles Gain: 17 dB Half power beam width: 22~ *)
Heating
Transmitter
Peak power: 1.2 MW Duty cycle: max. 4%
Transmitting antenna
Elements: 36 crossed dipoles Gain: 23 dB o Half power beam width: 15
Receiver, Adder, Radarcontroller, Tape unit
PRP: 1 ms, 4~ms Af: 9.38.10"~Hz, 2.34.10-2Hz Height resolution ~h: 3 km
SOUSY
The advantage of using the PRE antenna for reception and the Heating antenna for transmission is based on the different size (16 and 36 crosseddipoles) and therefore on the different shape of the radiation patterns. The product of both antenna diagrams leads to a side lobe reduction of more than 25 dB since the sidelobe maxima of one antenna coincide with the minima of the other one. Therefore, the probability of receiving oblique radar echoes from the E- and F-region at low elevation angles is largely reduced. Results and discussion The measurements were carried out for one or two hours per day during the period from Nov 29 to Dec 2, 1982. The radar was operated with different pulse repetition periods (PRP) of 1 ms and 4 ms, partly applying the pulse coding technique (see e.g. Schmidt et a l . , 1979). Fig. i shows a representative result obtained on Nov 30 from 1025-1100 LT and from 12041220 LT. The 3-dimensional plot presents 67 power profiles observed in the altitude range from 15 to 102 km. In addition to the well known layers in the mesosphere s i g n i f i c a n t radar echoes were detected for the f i r s t time at stratospheric heights. The mean decay of the echo power with height below 35 km is about 2.1 dB/km which is comparable with results derived from radar measurements in the VHF range (RUster et al., 1980). The echo intensity and the vertical velocity were derived from the power spectra after eleminating the DC peak resulting from ground c l u t t e r . Spurious signals induced by E- and F-region reflection were attenuated by oversampling and coherent integration which acts as a combfilter. The remaining interference was removed by spectral f i l t e r i n g . As demonstrated in Fig. 2 multiple scattering or reflection from E-region heights between 110 km and 140 km (three signal traces are denoted as "1", "2" and "3") do cause interference with atmospheric echoes at subsequent gatings, but at different heights. Since 166 pulses were coherently added to form one burst i t seems evident that E- or F-region echoes w i l l cause only an enhancement of the background noise. There is no indication for *) D. Leiulfsrud, Auroral Obs. Troms~, private communication
732
Short Paper
E
PRP: 2.1856-1921 12.1ms 82LT
7S.
N
I 2.12.82LT ~801-1826 /,ms
30.
15-
0
Fig. 3.
I 20
I 40
P/dB w/rns-~ 60
-0.2
0
I 20
I /.,0
PIdB
I
60
J -O2
0
wlms-1
Mean power and velocity profi|es measured with PRP of 1 ms and 4 ms.
Conclusion Radar measurements have been carried out on 2.75 MHz near Troms~ (Norway) to investigate structures in the middle atmosphere in the medium-frequency band. The results indicate the occurrence of 50 m-irregularities in the stratosphere which were observed for the f i r s t time. Acknowledgements
-
The authors would like to thank the Auroral Observatory (Troms~/
Norway) for the permission to use the antenna of the PRE f a c i l i t y during this radar experiment. The i n i t i a l discussion about this experiment with J. R~ttger and the constructive comments from R. R~ster and J. K1ostermeyer are gratefully acknowledged. References R6ttger J., Czechowsky P. and Schmidt G.
1979
Preprints 17th Radar Meteor. Conf., 349
Greqory J.B. and Vincent R.A.
1970
J. geophys. Res. 7__55,6387
Holt 0., Brekke A. and Hansen T.
1980
Proc. Vth ESA-PAC Symposium, Bournemouth, 387
R~ster R., Czechowsky P. and Schmidt G.
1980
Geophys. Res. Lett. ~, 999
Schlegel K., Brekke A. and Haug A.
1978
J. atmos, terr. Phys. 40, 205
Schmidt G., RUster R. and Czechowsky P.
1979
IEEE Trans. Geosci. Electron. GE-17, 154
Stubbe P., Kopka H., Lauche H., Rietveld M.T., Brekke A., Holt 0., Jones T.B., Robinson T., Hedberg A., Thide B., Crochet M. and Lotz H.J.
1982
J. atmos, t e r r . Phys. 44, 1025
732
Short Paper
E
PRP: 2.1856-1921 12.1ms 82LT
7S.
N
I 2.12.82LT ~801-1826 /,ms
30.
15-
0
Fig. 3.
I 20
I 40
P/dB w/rns-~ 60
-0.2
0
I 20
I /.,0
PIdB
I
60
J -O2
0
wlms-1
Mean power and velocity profi|es measured with PRP of 1 ms and 4 ms.
Conclusion Radar measurements have been carried out on 2.75 MHz near Troms~ (Norway) to investigate structures in the middle atmosphere in the medium-frequency band. The results indicate the occurrence of 50 m-irregularities in the stratosphere which were observed for the f i r s t time. Acknowledgements
-
The authors would like to thank the Auroral Observatory (Troms~/
Norway) for the permission to use the antenna of the PRE f a c i l i t y during this radar experiment. The i n i t i a l discussion about this experiment with J. R~ttger and the constructive comments from R. R~ster and J. K1ostermeyer are gratefully acknowledged. References R6ttger J., Czechowsky P. and Schmidt G.
1979
Preprints 17th Radar Meteor. Conf., 349
Greqory J.B. and Vincent R.A.
1970
J. geophys. Res. 7__55,6387
Holt 0., Brekke A. and Hansen T.
1980
Proc. Vth ESA-PAC Symposium, Bournemouth, 387
R~ster R., Czechowsky P. and Schmidt G.
1980
Geophys. Res. Lett. ~, 999
Schlegel K., Brekke A. and Haug A.
1978
J. atmos, terr. Phys. 40, 205
Schmidt G., RUster R. and Czechowsky P.
1979
IEEE Trans. Geosci. Electron. GE-17, 154
Stubbe P., Kopka H., Lauche H., Rietveld M.T., Brekke A., Holt 0., Jones T.B., Robinson T., Hedberg A., Thide B., Crochet M. and Lotz H.J.
1982
J. atmos, t e r r . Phys. 44, 1025