The JKT mast part of the file is common to the three sets of data,
and therefore the JKT mast set has no LOCAL part (so # symbol appears
in the space thus left free).
The three sets of data all contain the same JKT mast data which can differ
from one to the other due to a small difference in the timing of data
received, since the three PC clocks may have not been perfectly
synchronized.
The graphs
All the parameters are represented in monthly graphs. In addition, the
maximum, minimum and mean values over the month are given. All the values are
shown as a continuous line on the graph (if no data are missing) except Wind
Direction and Solar Radiation. For these two last parameters only discrete
points or dashes are plotted, which makes the graphs easier to interpret.
Where the line of a graph is interrupted the corresponding data were missing
or beyond the admitted limits for that parameter.
For each day and for all but the local parameters (i.e. not for local humidity
graps), the most complete set of JKT mast data is used; in other words, the
data for different days may come from different sets, from whatever
telescope had less problems in recording the data.
In the Solar Radiation graphs the unit used for the maximum, minimum and mean
values is W/m2, while the dashes of the graph represent the
Integrated Solar Radiation over the day in J/m2. This is because the
Integrated Solar Radiation would be expressed in
W x s / m2 = (J/s x s) / m2 = J/m2
Instruments and Data
Location of the sensors
On the JKT mast
- The main anemometer with wind speed and direction
- Hygrometer
- Thermometer
- Solarimeter
- Surface wetness sensor
- Dust monitor
- Barometer
Ground and underground level
- Soil temperature sensor
- Borehole temperature sensor
On the WHT and INT local stations
- Local anemometer with speed only
- Local external hygrometer
- Local internal hygrometer
- Local external temperature sensor
- Local internal temperature sensor
- Local surface wetness sensor
- Mirror temperature sensor
- Dewpoint sensor
Each group is also provided with:
- Solar panel
- Transmitter unit (only JKT mast)
- 12 V Electrolyte battery
In the control room of each of the telescopes are:
- Personal computer and display screen
- Receiver unit
- Dewpoint meter controller
Characteristics of the sensors
The characteristics of the sensors are listed here as given by the
manufacturer:
Anemometers
JKT main mast Anemometer
Type | Three cup rotor |
Range | 0 to 270 Km/h |
Accuracy | -+1% |
Operating temp. | -40 °C to +70 °C |
Location | Top of the JKT main mast |
Local Anemometers
Type | Three cup rotor |
Range | 7 to 245 Km/h |
Accuracy | -+1% above 11 Km/h |
Operating temp. | -40 °C to +70 °C |
Location | Roof of INT and WHT telescope buildings |
Vane
Type | Continuous rotation wire wound potentiometer |
Range | 0 - 355 degrees (0=North, 90=East) |
Accuracy | -+5 degrees |
Sensitivity |
10 deg offset with 4.5 Km/h of windspeed |
Operating Temp. | -20 °C to +70 °C |
Location | Top of the JKT main mast |
Hygrometers
Internal and external Hygrometer
Type | Capacitive |
Range | 0 - 100 % |
Accuracy | -+2% at +22 deg |
Operating Temp. | -40 °C to +60 °C |
Location | Inside of each telescope dome, INT and WHT local stations and JKT main mast |
Thermometers
Air Temperature thermometers
Type | Platinum resistance |
Range | -25 C +60 C |
Accuracy | -+0.35 °C within -20 °C +50 C |
Location | All the three stations |
Soil and borehole thermometers
Type | Semi conductor current generator type |
Range | -25 °C +60 °C |
Accuracy | -+0.5 °C over -20 °C +50 C |
Location | Close to JKT main mast |
Solarimeter
Type | Pyranometer of silicon pn junction type |
Range | 0 - 1500 W/m2 |
Accuracy | -+2 W/m2 |
Response time | 17 sec. to 66% of final reading |
Operating Temp. | -25 °C to +70 °C |
Location | JKT main mast arm |
Surface wetness sensor
Type | Three element carbon electrode |
Range | Digital signal, 0-1 |
Accuracy | Not specified |
Response time | Not specified |
Operating Temp. | -10 °C to +55 °C |
Location | JKT main mast arm and INT and WHT local stations |
Dust monitor
Type | Light scattering optical device |
Range | 0 mg/m3 to 2 mg/m3 (the range 0 mg/m3 to 200 mg/m3 is also available) |
Sensitivity | -+10 microgr/m3 |
Response time | Constant 1 sec or 10 sec |
Operating Temp. | 0 °C to +40 °C |
Location | JKT main mast electronics box |
Barometer
Type | Silicon bridge |
Range | 660 - 860 mbar |
Accuracy | -+0.3 mbar |
Operating Temp. | -20 °C to +50 °C |
Location | JKT main mast bottom box |
Dewpoint meter
Type | Direct detection of condensation on cooled mirror |
Range | From 0 °C to 40 °C below ambient temperature |
Accuracy | Not specified |
Operating Temp. | -40 °C to +60 °C |
Location | Close to each of the telescope primary mirrors |
Assessment of data quality for the years 2000-2002
The whole system has proved to be quite good and most of the sensors
have shown no evidence of malfunctions since installation. The sensors
which have been tested by analysis of the data are: barometer, hygrometers,
anemometers, thermometers. Visual checks have been performed on the dust
monitor, wetness sensor, dewpoint sensor, solarimeter.
Pressure
Our sensor has been compared with a mercury barometer on site. Our readings
are mostly low and the mean error (during 2000-2002) is estimated to be about
0.6 mbar, with a maximum of 2.2 mbar and minimum of 0.1 mbar.
This error has been remarkably stable after 1998
(see graph).
Wind
Comparisons between the JKT anemometer and the one at the Meridian Circle,
which has been working on site for over ten years, show good agreement, if one
allows for small differences due to the different locations.
The structure of our device leaves a gap from 356 to 359 (included) degrees.
Any value falling within this interval is set to 0 degrees.
Some data were lost during the winter due to freezing of sensors
mainly during January and December.
The wind speed by all the anemometers always looks quite consistent with
handhold anemometer readings. A difference between the two of (say) 5 Km/h
may be accepted as due to the handhold instrument always being lower than
the fixed anemometers.
Temperature
Thermometers, either air or soil ones, always showed consistent values with
each other. In November 2002 (19th) the borehole sensor failed and we have
no data for the rest of November and December.
Solar radiation
A rough check of the Solarimeter readings compared with the Solar Constant
always showed sensible values. The monthly graphs show a regular and smooth
performance. The only error I could detect regards the moment the Sun appears
after being obscured by cloud. The instrument cools when the Sun is hidden
and gives slightly exaggerated values at the moment the Sun strikes it again.
These jumps are intrinsic of the working principle of the sensor and have
been filtered out by showing the Integrated Solar Radiation.
The shadow of one of the security ropes holding the mast falls onto the
solarimeter for a few minutes around 08:30 UT. This, however, is not
detectable on the graphs.
Humidity
Hygrometers, when checked during a stable period, proved to be quite reliable;
their error, usually around 2%, gets bigger for either extremely low or high
values (up to 15%). The WHT external hygrometer has been substituted on
November 7th 2000 as it was reading about 3% less with very high humidity.
Power supplies
The solar panels work very well, the only problem is that the glass covers are
quite fragile and during winter they are liable to get broken by ice falling
from further up the mast or by water on the panel expanding when it freezes.
The batteries usually last well enough; a failure happened during a severe wind storm
in December 2002, which blew off the solar panel from the INT and the local
station ran out of power.
Data losses
The three telescopes' sets of data contain the same JKT mast data which can
differ from one to the other due to a small difference in the timing of data
received, since the three PC clocks may not have been perfectly synchronized.
The graphs of the JKT mast variables (i.e. all but INT and WHT local humidity
graphs) were made using data from both set of files, WHT files and INT files,
filling the gaps of one with data from the other. The resulting data loss during
the year 2001 has been about 7.5%. During the year 2002 it has been about 8.7%.
Most of the losses during 2002 were due to failure of the recording PCs and not
to problems with the meteorological system itself.
The JKT set of data is kept only on the PC disk and is not available online.
© 2002 Isaac Newton Group of Telescopes
Marco Azzaro