1 / 6

Some considerations about Chopping on SOFIA and the Water Vapor Monitor

Some considerations about Chopping on SOFIA and the Water Vapor Monitor. Eric Becklin Chief Scientific Advisor SITR 28 Sept 2009. Why do we Chop?. Background could be 10 4 larger than signal Background has 1/f type noise Detectors have some 1/f noise. A. B. B. A.

sabin
Download Presentation

Some considerations about Chopping on SOFIA and the Water Vapor Monitor

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Some considerations about Chopping on SOFIAand the Water Vapor Monitor Eric Becklin Chief Scientific Advisor SITR 28 Sept 2009

  2. Why do we Chop? • Background could be 104 larger than signal • Background has 1/f type noise • Detectors have some 1/f noise

  3. A B B A We chop at ~10Hz between two sky positions f(A) = Sky|A + Tele|A + f(star) f(B) = Sky|B + Tele|B Subtract f(A) – f(B) = f(star) +[Sky|A – Sky|B] Great large gain ≥100 DC: integrate all noise AC: chop only noise in Δf

  4. Chopping at what frequency? • With SOFIA we might (probably will) have certain frequencies we want to avoid • Telescope or cavity resonance • Noise spike at that frequency • Instruments MUST have a way to change chopper frequency • Need to ask each instrument how they will do this • FORCAST, GREAT, FIFI-LS • FLITECAM needs a chopper interface ( λ< 3um )

  5. Early Availability of the Water Vapor Monitor • The GREAT Team has requested the Water Vapor Monitor for Short Science 2 • Final WVM configuration not possible until aircraft mission systems are finished in Segment 3 downtime • Can a reduced capability Water Vapor Monitor be of use to GREAT? • Somewhat conflicting Early Science requirements/desirements • Clear this up in this meeting • Have been talking with the Platform staff to see what additional work might be done to allow the existing WVM system to be used • Same mission systems staff that are on the schedule critical path • Need to visit DAOF to definitively clear up uncertainties in what was done by L-3

  6. WV Measurements from Satellites • GOES-West provides 24/7 coverage of the Pacific and the western CONUS • Is not real-time, but some WV data can be extracted 24 hours later • Satellite has a sounder instrument • 18 IR channels, 1 visible, IR sensitivity 1°K absolute, 0.25°K relative between channels • Spatial resolution is 10 x 40 km from geosynchronous orbit • CIMSS center calculates dewpoint temperature vs. altitude every 40 minutes at 250, 200, 150, 135, 115, 100 mb, (corresponds roughly to altitudes of 33,000 to 54,000 ft.) • Can derive estimate of WV overburden at least up to 54,000 ft. • Need to compare accuracy of satellite estimates vs. degraded early WVM

More Related