J. Stutzki, KOSMA,herschel.esac.esa.int/twiki/pub/Public/Calibration... · 2012. 3. 9. · J. Stutzki, KOSMA Jan 20th, 2012 HcalSG, Workshop Jan 2012: Cross Calibration GREAT/SOFIA

Page1Jan 20th, 2012J. Stutzki, KOSMA HcalSG, Workshop Jan 2012: Cross Calibration GREAT/SOFIA and HIFI/Herschel

Cross Calibration GREAT/HIFI

Cross Calibration GREAT/HIFIJ. Stutzki,

KOSMA,

I. Physik. Institut, Universität zu Köln


SOFIA: early science program

• demonstrate science capabilities and basic operationthree science instruments

- FORCAST mid-IR camera (PI: T. Herter; Cornell)

- GREAT heterodyne spectrometer (PI: R. Güsten, MPIfR; KOSMA)

- HIPO fast occultation camera (PI: T. Dunham; Lowell Observatory)

guaranteed time and open time program- e.g.: GREAT

› 17 science flights (2 failures; partially reduced efficiency)including

» observatory characterization flight

» 2 instrument commissioning / engineering flights

» 6 GT / consortium flights

» 8 OT flights

publications in prep- ApJ special volume: FORCAST

- A&A special volume: GREAT

GREAT first-light press release


GREAT

GREAT: German REceiver for Astronomy at Terahertz frequencies

PI-Instrument funded and developed by

MPIfR (2.7THz channel)

R. Güsten (PI)S. Heyminck (system engineer) now: Christophe RisacherB. KIein (FFT spectrometer)MPIfR Engineers (electronics, LO-mechanics)

KOSMA (1.4/1.9THz channels)

J. Stutzki (Co-PI)U.U. Graf et al. (1.4 &1.9THz LO, Optics)K. Jacobs et al. (mixers @1.9THz & 2.7THz)R. Schieder et al. (array-AOS)

DLR-Berlin (4.7THz channel)

H-W Hübers et al. (IF, cold-Load, …)

MPSP. Hartogh et al. (CO-PI; CTS)

Prior to short-science flight #3:

GREAT Team entering the plane

MPIfRKOSMAMPSDLR-Berlin


GREAT

• modular heterodyne receiver system in the 1.2 – 5 THz frequency rangechannel independent components

- main structure : optics-compartments, LO-compartments, electronics rack

- cryostats : liquid Helium/Nitrogen cooled wet dewar

- calibration unit : liquid Nitrogen cooled cold-load, ambient temp. hot load

- control-electronics : optics, mixer-BIAS, power-supply

- IF-system : input 4-8 GHz, output 4 times 1.55 – 2.65 GHz for AOS and CTS

- backends› AOS-system : 8 times 1.1 GHz, 1 MHz resolution› CTS-system : 2 times 220 MHz, <60 kHz resolution› FFTS : 2 times 1.5 GHz, 213 kHz resolution

• operating up to two independent receiver channels simultaneouslychannel specific components

- optics : LO-coupling, matching mixer beam to the telescope focal plane

- LO-system- mixer device : HEBs so far for all GREAT channels

PI: Rolf Güsten, MPIfR Consortium: MPIfR, KOSMA (J. Stutzki), MPS (P. Hartogh), DLR-WS (W.Hübers)


GREAT


GREAT optics lay-out


Load-Window fringes

GREAT calibration scheme

• standard heterodyne instrument calibration

double sideband; assumption: sideband ratio = 1

HEB mixers: automatic compensation for shift in bias (direct detection)

gain [counts/K] from HOT-COLD

Trec

from Y-factor on HOT/COLD

ηfwd

from optics, lab-measurements, and Tb,sky

(Elev)

sky transmission from OFF- atmospheric model fit

assumptions:› T

sky = T

amb

› τν from model as function of p

amb, T

amb

ηmb

from Mars

Mars @1337 GHz


GREAT: atmospheric calibration

• atmospheric models:AM (S. Paime, CfA)

- very sophisticated and flexible

ATRAN (S. Lord, IPAC)

- lacks collision induced transitions from N2, O

2 (dry continuous opacity)

- heritage from KAO / AIRES

ATM (J. Pardo)- does not properly and completely cover transitions > 1.5 THz

- good empirical “calibration” on Manua Kea and Chajnantor/ALMA

MOLIERE (J. Urban, Chalmers; N. Schneider, Saclay)- similar features to AM

none gets the dry continuous opacity at SOFIA flight altitude compatible with GREAT dual-frequency observations !?!?


atmospheric models: comparison

AMATRANMOLIERE

AMATRANMOLIERE


atmospheric models: comparison

AMATRANMOLIERE

AMATRANMOLIERE

shows up in image sideband for [CII] tuning



high excitation water linefrom upper atmosphere:

get weaker with larger opacity

(image sideband)

two observations:different tuning,different elevation/ transmission

example of sky-hot measurements (NGC7023 observations)



example: NGC7023 observations

signal-sideband opacity τν

different elevation/ transmission

line-of-sight opacity up to 0.22


GREAT/SOFIA – HIFI/Herschel cross calibration

goal: compare intensity (profile, integrated intensity) forpoint-like source

- independent of beam-imperfections

extended source- insensitive against pointing errors

opportunities (observed with both GREAT and HIFI):NGC 7027 [CII], CO high-J:

- point-like

- SOFIA at time of observations had pointing problem (dbs) → 7” off

continuum of compact HII-regions (absorption measurements)- about half a dozen in common

- baseline/standing-waves allow accuracy of only about 25% (Christophe Risacher)

NGC 7023 [CII]- extended, small velocity gradient



• NGC 7027 [CII], CO high-J:- point-like


HIFI 3x3 map, 5” spacing

GREAT dbs, single pointGREAT dbs, single point

beam size correction: FWHM 11” vs. 15” !



goal: compare intensity (profile, integrated intensity) forpoint-like source

- independent of beam-imperfections

extended source- insensitive against pointing errors

opportunities (observed with both GREAT and HIFI):NGC 7027 [CII], CO high-J:

- point-like


continuum of compact HII-regions (absorption measurements)- about half a dozen in common

- baseline/standing-waves allow accuracy of only about 25% (Christophe Risacher)

NGC 7023 [CII]- extended, small velocity gradient


HIFI: WADI (V. Ossenkopf)

cross calibration: NGC 7023 observations, [CII]



HIFIGREAT

TA*-scale

note:extended source

“error” beam pick-up


GREAT/SOFIA beam @ 1900 GHz


correction derived from calculated beam patter


GREAT/HIFI cross calibration: Summary

• NGC 7023 [CII] allows detailed comparisoncorrection for first (& second side-lobe) necessary

agreement within 14% - consistent with atmospheric calibration uncertainties

- consistent with beam-efficiency uncertainties

• NGC7027 [CII]correction for beam filling

large uncertainty due to pointing correction

agreement within 20%

• continuum point sources not suitable due to standing waves/baseline problems

• outlook/improvementsneed comparison with bright point-like line source

measure radial power distribution in main beam

Documents

J. Stutzki, KOSMA,herschel.esac.esa.int/twiki/pub/Public/Calibration... · 2012. 3. 9. · J. Stutzki, KOSMA Jan 20th, 2012 HcalSG, Workshop Jan 2012: Cross Calibration GREAT/SOFIA