SCUBA opacity calibration
Atmospheric corrections for SCUBA data
There are three basic ways to correct JCMT data for the opacity of the
atmosphere (Tau-correction). First, there are the
JCMT-Skydips. They are available as normal JCMT data files and
can be reduced with SURF and ORAC-DR. Second there is the
JCMT-Water-Vapor-Monitor (WVM). It sits in the Receiver Cabin
and measures Tau every 6 seconds. It is pointed just slightly off the
main beam. Third there are polynomial-fits to the
CSO-Tau-Dipper. The dipper is located at the CSO and makes a skydip
every 10 minutes at an azimuth of 316 Degrees. The data is fitted with
a polynomial because the accuracy of the single measurements is
poor. All three measurements are well calibrated against each
other. Because the resolution of the WVM is highest and it is pointed
in the direction of the main beam, it is in most cases probably
slightly superior to the other two. Further improvements of the
atmospheric correction are currently ongoing, as is the documentation
of it available.
Skydips and Tau information
You can access the data from the JCMT-Water-Vapor-Monitor here.
The improvement of the WVM-Data is ongoing. A full documentation will be published soon. Meanwhile please contact Bernd Weferling. for questions. As a first reference here are some first(!!) results from the calibration of the WVM to the CSO-Tau-Fits.
Polynomial fits to CSO data
- Note on Fits after July 11 2003: The calibration of the 225-CSO-Dipper after the repair has been verified and hasn't changed. Fits will be provided now again with csofit.dat. See the verification of the calibration here . Shown are 420 pairs of JCMT-Skydips at 850 micron and simultaneous polynomial fits to the 225-CSo-Dipper between July 2003 and July 2004. The blue 'Old' represents the old canonical calibration which we continue to use. The red 'New' line represents the relation between July 2003 and 2004. Both agree within the margin of error.
- Read an explanation of how to use
these fits to calibrate your data.
- Access the polynomial fits. The file csofit.dat contains all the fits in the archive in the style of the nejpolys.txt files. This file can be used with ORAC-DR. Read the explanation on how to update your version of ORAC-DR. If for a given night no fit has been provided (there is a variety of reasons for that) one can be requested via e-Mail. Please also send me an e-Mail if you wish to discuss a specific fit.
- Overview SCUBA calibration 2003.
- An interface to the raw CSO data is available from the
JCMT or the