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Raymond_TSE

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發表於 2013-6-14 22:53 | 只看該作者

Remote Telescope Observatory-Realtime Weather Charts

Dear all,

With the input from Angus Lau and the tremendous assistance from Kenneth Yan, we are able to present the real-time weather charts of Remote Telescope Observatory (RTO) at Sai Kung.

The RTO is close to Pak Tam Chung (about 6km NW of Pak Tam Chung).

The real-time weather charts (2 hrs duration each) can be seen at :-
http://www.raymondtse-lawyer.com ... ry/observatory.html

The speed to download the weather charts may be slow due to bandwidth limitation.

Raymond Tse
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Raymond_TSE

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發表於 2013-6-17 01:39 | 只看該作者
本帖最後由 Raymond_TSE 於 2013-6-17 01:40 編輯

Dear all,

SQM (un-calibrated yet as off-set value has not been added) Graph (magnitude per sq arc sec) is also added to the weather charts :-

http://www.raymondtse-lawyer.com ... ry/observatory.html

Raymond Tse

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Raymond_TSE

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3#
發表於 2013-6-20 11:02 | 只看該作者
The SQM has now been calibrated by setting an offset.

Best reading yesterday night (with some thin sky haze) was 20.05, or about 5.5 near eye limiting magnitude.

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terryfai

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發表於 2013-6-25 01:36 | 只看該作者
Would you please share to us more about the calibration of SQM?
How you define an offset?

Terry Wong
http://www.facebook.com/apterryfai

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Raymond_TSE

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發表於 2013-7-5 03:09 | 只看該作者
本帖最後由 Raymond_TSE 於 2013-7-5 03:19 編輯

No-IP routing is now used to prevent frequent changes of IP address.

SQM meter graph will be updated soon after the computer's CPU heat sink is replaced to prevent overheating of CPU; while conversion table of sky brightness magnitude to near eye limiting magnitude is added for easy reference.

http://www.raymondtse-lawyer.com ... ry/observatory.html

Dear Terry,

Since the SQM is placed indoor and pointing out of window, the glass and part of the indoor structure will absorb some light and thus the reading for indoor placement must be higher (darker) than when the meter
is placed outdoor without any enclosure.

To calibrate, simply place the meter indoor for some time to check its average readings. Then place it outside naked to measure the average readings without any enclosures. The difference is the offset.

Use this offset value in the SQM Pro graph and then get the calibrated readings in graphic display. Thus meter placed indoor (for more durability and protection) will have similar effect as if it is placed outdoor naked.

Raymond Tse

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terryfai

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6#
發表於 2013-7-8 03:28 | 只看該作者
回復 5# Raymond_TSE


Dear Raymond,

Thanks for sharing the idea to us.
I agree with your method on offset compensation due to the light attenuation by the movable enclosure window.

Meanwhile, for curiosity, have you ever tried to compare the value between yours and the hku's which is set at rooftop of iObservatory in Pak Tam Chung?
http://nightsky.physics.hku.hk/m
I would like to ask if there is any big difference in values between them within 6km distance.

Furthermore, for maintenance and working accuracy of SQM,
may I ask how old yours is?
There may be a possible frosted blue filter inside SQM causing inaccurate reading of the output. (+ 0.7 ~1.5 mpsas)
Also, firmware 17 or more can let the output more accurate while it was measuring below 16mpsas since averaging algorithm is added on it.

Terry
http://www.facebook.com/apterryfai

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Raymond_TSE

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發表於 2013-7-11 13:36 | 只看該作者
本帖最後由 Raymond_TSE 於 2013-7-11 13:46 編輯

The SQM graph is now resumed to normal operation.

Last night (10-07-2013) we had a clear sky with little clouds. Ground surface visibility is also very high with good seeing.

Sky brightness was about 19.98 at the best.

The graphical phase is now complete. The next phase will be webcast of analogue image of all-sky camera via RCA signal.   Any webcast expert for analogue video image ?

Dear Terry,

I have not gone into technical comparison of accuracy of the SQM meters themselves. My version is LAN version bought in about March 2010 with a lens at the middle.

I believe the factory would have a slight tolerence of variation even if 2 meters are pressed at the same time at the same location.
Their Pak Tam Chung reading last night was 19.9. Nearly the same as  my 19.93 to 19.98 range.

I take the reading every 5 min but average them in 15 minutes. Then present each 15 min averaged reading (each less the offset of 0.925) in graphical display.

I am not sure whether Pak Tam Chung's SQM is also calibrated with offset if their meter is placed under a plastic dome/plate

If arrangement can be made with another SQM meters, it is interesting to compare 2 or more SQM meters, may be at a star party.

Raymond Tse

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terryfai

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8#
發表於 2013-7-11 19:28 | 只看該作者
回復 7# Raymond_TSE


    Dear Raymond,

It is happy to see that SQM graph is working now and it can be used as another reference to decide if PTC is suitable for stargazing that night.
Meanwhile, another good news is the only small differences between yours' SQM-LE with Pak Tam Chung (PTC) 's one (SQM-LE) is observed,
the value definitely lies within acceptable range.

PTC's SQMLE
Since PTC's was put inside the weatherproof box which has a circular opening covered with high light-transmitting glass,
light from the sky entered this opening and measure the night sky brightness (NSB) .
Attenuation of glass changed gradually and slowly with time, about 0.05 - 0.2 mpsas (offset) .
Their "real time" (w/o offset subtraction) NSB shown on the page is median within 15 minutes, under 1-min sampling.

Under this setup, PTC's SQM-LE is thus exposed to the light both daytime and nighttime.
If you look into the SQM-LE, you can find a 3mm x 3mm blue color opaque filter in front of the sensor.
Under long term usage, say 2 years or more, that filter would probably become non-transparent and
causes incorrect measurement  that I am worried about.

Since hku is leading the project and I am not sure if they are still curious to another meter located in PTC.
I just would like to share my experience of using SQM-LE here.

At last, your RTO is well designated and professional,
I am looking forward to your masterpieces.

Wish having starry nights.
Terry Wong
http://www.facebook.com/apterryfai

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