Caltech EM27/SUN FTS

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Version as of 21:54, 19 Sep 2020

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We anticipate using this mobile intrument in conjunction with TCCON instruments (e.g. the one at Caltech) to provide ground validation for and check for biases in OCO-2.   We also anticipating using this instrument to examine emissions of various gases from point locations and sources in the South Coast air Basin (SCB).



Resolution: 0.5 cm-1

Geometric distance moved: 0.45 cm

Optical path difference: 1.8 cm

Range: ~40009000 cm-1

Gases measured (expected): CO2, CH4, CO, H2O, N2O, O2

Naming convention: 2 letter site id is cn while the instrument is at the Caltech site and mn when it is mobile.  Spectra are thus named as either: cnYYYYMMDDs0e00a.XXXX or mnYYYYMMMDDs0e00a.XXXX depending on location.  In this convention YYYY is year, MM is month, DD is day of month, and XXXX is a four-digit number.





  • USB GPS (Amazon)
  • Compass (Dick's Sporting Goods)
  • Bubble level (from OSH)
  • Extension Cord, 100 ft (Home Depot)
  • Cord storage (Home Depot)
  • Surge Protector (Home Depot)
  • Laptop ordered from Amuras Computers (PANASONIC TOUGHBOOK 53 (CF-53SALLYLM)), May 13 Programs to install
    • OPUS (by Bruker)
    • Suntracker (by Bruker)
    • MATLAB
    • Office Suite
    • WinSCP
    • PuTTY
    • Firefox
  • Router
  • Networking cables
  • Weather station (we have an extra Zeno lying around in lab), for pressure, humidity, and temperature and hopefully wind speed/direction
  • Cart and/or encasing.  Needs:
    • Hold EM27 + cords + etc., while making measurements and storing
    • Transport
    • Some protection from weather ?
    • Absorb some bumps/shocks
    • Portable (for loading in car)

Car suggestions:  


(would prefer larger wheels)

Also, floor locks, adjustable (to level cart and keep in place) 



Considering for future (depending on goals/needs)

  • Portable power source, estimated draw of 75130 W.  ESTIMATES  EM27: ~40 W (avg) 80 W (max),  laptop: 1560 W (may be able to run off own battery),  Weather station: ~10 W ??,  Router: ~1020 W (may be unnecessary when going portable, depends on if everything can be connected to laptop).  OPTIONS:
    • UPS ~$40$200, estimate runtime 1–4 hrs
    • YETI 400 ~$500, estimated runtime 2.56.5 hrs
    • Ark-pak ($400) + battery (~$100), estimated runtime: 12 hrs/full day depending on battery capacity
    • DC/AC inverter ($40) + battery charger ($70) + battery ($100), estimated runtime: 12 hours/full day depending on battery capacity
  • HCl Calibration cell (slot for a 40 mm diameter, 40 mm length cell but may need external), or need to work on method to watch instrument line shape (ILS)




May 28, 2014

Baron from Bruker unpacked and set up the initial install of the instrument.  Total time was less than 4 hours.  Had some problems with the ellipses in the camtracker progam.  Had to make adjustments to Configureation file, located in the same directory as the tracker program.  Changed settings to what was in the manual, and then made additional adjustments from there.

Acquired lamp spectra with filter in place to look for ghosts.  Doubling ghost was present as were laser sampling error (LSE) ghosts.  Tried to eliminate them using the xsm command, but there was a bug so we were unable to.  Camille will email Bruker.

May 29, 2014


Tried adjusting the scanner velocity to see its effect on LSE ghosts.  The low-pass filter was set to match the scanner velocity.  For the EM27, 20 kHz gave the smallest LSE ghosts.  Largest ghosts were seen at 40 kHz, then 10 kHz, with 20 kHz and 5 kHz having the smallest ghosts (on the order of twice the noise in 10000 scans, the ghost to parent ratio GPR was on the order of 7x10-5).  Doubling ghosts did not appear to change.

Also, for future reference it appears that in order to save all of the data in opus you must set Sample Scan Time to 2 (or some even number).  The up and down pendulum motion looks like it is saved as 2 side by side interferograms.  If the Sample Scan Time is set to 1 then data is only recorded as the pendulum moves in one direction.  Time required to record an interferogram (20 kHz, 0.5 cm-1 resolution) was 5.9 seconds wheter Sample Scan Time was set to 1 or 2.  This seemed to be true even if Forward/Backward was set for Acquisition mode (we should double check this).