1. Celestial and atmospheric H2O detection by direct RF sampling
IVTW in Bologna, Italy
, October 11, 2017
Celestial and atmospheric H2O detection by direct RF sampling
Noriyuki Kawaguchi
Professor Emeritus
National Astronomical Observatory of Japan
Y. Kohno, T. Oyama, NAOJ
T. Nagasaki, KEK, T. Maeda, JAXA
K. Harada, Y. Chikahiro, Elecs

2. Contents Development of a high speed AD converter
Direct RF detection of astronomical H2O maser emission
Water Vapor Radiometer
Direct detection of atmospheric H2O emission
Volcano fume monitoring

3. The use of the InP HBT technology
Development

4. 30-GHz RF sampler, a trial unit
A trial test unit of a high speed sampler.
Clock Distributor
3-bit ADC
1:16 DEMUX
Analog signal
Input
DC voltage
generator

5. RF Direct sampled Digital Spectrum of 4-GHz BW
The first successful result in 2007.
20.48GHz
Fs=8.192GHz
24.576GHz
Red Dots: RF Direct Digital Spectrum
Green Dots: Analog Spectrum
20GHz
25GHz

6. Sampling Jitter 0.2-psec jitter
Sampling jitter is a cause of fringe phase fluctuation.
0.2-psec jitter
2x10-13

7. Astronomical Application
H2O maser in 22GHz
Astronomical Application

8. W49N on Nobeyama 45m Observations were made on August 8, 2008 Digital
RF direct sampler
Digital
Spectrum
Conventional

9. Water Vapor Maser, W49N
Observed by VERA, Honma(2004)

10. W49N on NRO 45m detected without frequency conversion
Direct detection ( GHz)
Spectrum after frequency conversion
LO=( )-GHz signal converts a 22-GHz Signal to a GHz signal. The IF signal Is digitized at a speed of GHz (over sampling), then Fourier transformed with 512K spectrum.
A GHz (BW=4.096GHz)
signal is directly digitized at a sampling
rate of 8.192GHz, then Fourier trans-
formed with 512K spectrum. The spectrum
order is inverted.

11. GIGA Sampler for RF Sampling Now Commercial Available
Presented by
Harada Kenichi
Elecs Industry Co.,Ltd., Japan

12. 16Gsps × 3bit ENOB (Effective number of bits)

13. Water Vapor Radiometer
For astronomy, Geodesy and Volcanology
Water Vapor Radiometer

14. Absorption in Radio Astronomy
The correction on tropospheric absorption is a key for good imaging and for deducing absolute brightness.
40K (

15. Uncertainty in radio brightness

16. A variable star or sky fluctuation?
-1.3dB
←1.2Jy
(1.6Jy
@l=30deg)
←1Jy
-0.43dB
Two weeks
Forkman_Onsala_2003

17. VLBI vs WVR WVR delay VLBI delay 1 -1 2 Delay (mm) Time (seconds) 1001 -1 2
Delay (mm)
Time (seconds)
100
200
400
300
David A. Tahmoush and Alan E. E. Rogers, Correcting atmospheric path variations in millimeter wavelength very long baseline interferometry using a scanning water vapor spectrometer, Radio Science, Volume 35, Number 5, Pages 1241–1251, September–October 2000

18. KEK radiometer
KEK: High Energy Particle Acceleration Research institution

19. Analog spectrum by KEK
Noiser (rms)=

20. Digital Spectrum 0.1 K ↔ 0.5 mm in EPL
0.1 K ↔ 0.5 mm in EPL
0.01 K ↔ 0.05 mm in EPL by averaging 128 FFT points

21. Time profile at the spectrum peak
F=22.7 GHz (FFT point=56)
Rms=0.13 K
0.13× × 3× =𝟏.𝟕× 𝟏𝟎 −𝟏𝟑
DSN WVR: 5x10-12
SHAO WVR: 5x10-12
UoB WVR: 1.7x10-12
HALCA: 1x10-12
UoB Corr WVR: 1x10-12
DSN AWVR: 6x10-13
Australia WVR: 4x10-13
H. Maser: 1x10-13
0.13 K ↔ 0.6 mm in EPL
The precision is the best in the world!

22. Water vapor monitoring in a volcano fume
volcanology

23. Disaster in Ontake in 2014, Japan
56 confirmed dead and seven still missing
After deadly eruption, Japan ponders how to improve predictions,
By Dennis Normile Oct. 17, 2014, Science News

24. Gas Composition
Decrease in the water vapor, volcanologists says that it is a sign of eruption.
Burton_2007

25. H2O monitoring of a volcano fume
Bryan_2016
1.5-K increase
1.5K in Tb ↔ 6.8 mm in EPL↔1 mm in PWV ↔ 1 kg/m2 in column density

26. Summaries A high speed RF sampling system was developed.
Good agreement between digital and analog spectra was obtained.
W49N spectra were successfully detected with RF sampling
A new digital WVR is now being developed.
The digital spectrum noise is estimated to be from 0.1 to 0.3K at integration time of 1 second.
The noise is estimated to be 0.13K. It shows the best stability in the world.
New application to Volcanology

27. supplement

28. Higher Order Nyquist Sampling6 12 18 24 30 8 16 28 ① ② ③
Waveguide(WRJ240) Pass Band 26
Freq.（GHz）
RF Spectrum ＃１ ＃２ 20
8Gsps Digital Spectrum 4