VERA UM @Mizusawa
2017.11.4

Current State of WVR
Development
N. Kawaguchi
Y. Kohno, T. Oyama, S. Suzuki(NAOJ)
T. Nagasaki (KEK)
T. Maeda (JAXA)Contents• Scientific Importance– Correction of atmospheric absorption for source
brightness– Correction of delay for geodetic/astrometric VLBI– Correction of phase fluctuation to keep longer
coherence time

• Performance Criterion– ASD statistics– World Ranking• Cost Effective Design and Performance

Uncertainty in radio brightness

The spectrum index is an
important measure to know AGN
activity.
Drawn by Yuzhu Cui-san3

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

4

VLBI vs WVR
2
WVR delay
Delay (mm)1VLBI delay
0-1
100

200
Time (seconds)

300

400

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

5Stability of SHAO WVRFirst 6-hour on May 31, 2016

5x10-122.5x10-13

1.2x10-14

Stability of Australian WVR
4x10-13
Indermuehle_2013
7x10-14‘Stable’atmosphere1.5x10-14

0.8x10-14
1x10-14 by Kawaguchi’smodelStabilities of world WVRｓ
Name
DSN WVRSHAO WVR
University of Bern （UoB)
HALCA Phase Transfer
UoB Correlation WVR

DSN Advanced WVR for Cassini of NASA
Australian WVR
Hydrogen Maser Oscillator

Stability @ 1second
5 x 10-12
5 x 10-12
1.7 x 10-12
1.0 x 10-12
1.0 x10-12

6 x 10-13
4 x 10-13
1 x 10-13

Cost Effective DesignThese commercial
available WVRs areexpensive, 200K USD
or more.

Radio Metrics (USA)RPG (Germany)• No driving motors, to be mounted on a radio telescope• No GPS receiver, to be used GPS at a VLBI station• No optical monitoring system• No weather sensors, to be used information from a VLBI
weather station• No high speed AD, to be shared with that in a VLBI station

KEK Experiment2016.12

Rms=0.13 K

0.13 × 4.5
128 × 3 × 1011

= 1.7 × 10−13

The best stability in the world!

The error of 0.1 mm is corresponding to the EPL error of 0.45mm.
By fitting 256-point of spectrum, one order of magnitude better error
can be expected.

Roof Top Experiment

Water Vapor Spectrum
0.1K_rms over 19-25GHz

Op Range2017.7.3

Time Profile
0.08K rms at 22.2615GHz,
A rapid change of liquid
absorption was observed.

• The almost same stability as the KEK
experiment was achieved.
• Linearity has already been tested.
• Stability test of Trx is now under going.

Conclusion• The WVR development sponsored by NAOJ isgoing on track.
• The best stability in the world is expected.
• Remaining works– Assembling to a unit and set it on Mizusawa 20m– One more unit for a VERA station or Kashima 34m– VLBI/WVR experiment– A ceramic package for future applications including
water vapor detection in a volcanic fume. The
astronomical technique of imaging will be introduced.

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 News13

H2O monitoring of a volcano fume
Bryan_2016

1.5-K increase14

1.5K in Tb ↔ 6.8 mm in EPL↔1 mm in PWV ↔ 1 kg/m2 in column density