GBT Pointing Model 2007 (5c)
This collects data used to derive the GBT pointing model 5c, which is currently in use.
(F. Ghigo, Sept 2010)
Data files from which the model was derived
Az/El and focus files have values separated by commas ("csv" files)
Some comments on the contents
- ProjectID : encodes the date (e.g. 070926). The dataset comprises observations on 11 different days,
September 3, 4, 5, 6, 7, 13, 15, 20, 21, 23, and 26, of 2007.
- ObsType : the sequence is forward and reverse azimuth scans (AzF, AzB), the azimuth pointing correction is updated,
then up and down elevation scans (ElF, ElB). The normal sequence is 8 lines, these 4 scans at both LCP and RCP
polarizations, in a sequence of 4 scans of sequential scan numbers ("Scan" column).
To get a single offset vector, just take each sequence (start with AzF, end with ElB) and average the "Value" column
over all the Az scans to get the cross-elevation offset, then average over all the El scans to get the elevation offset.
Note: some of these sequences are not complete; you may choose to ignore the incomplete ones, or to average whatever data is there.
- PointingModel : "none" means the "Value" is the difference between Observed and Instrumental place.
- Peak and Width: each observation is a scan across a calibration source; the plot of amplitude vs time for one of these
scans is approximately a gaussian. A gaussian fit is done to each scan to produce an amplitude (Peak), width (Width), and
offset from the predicted position ("Value")
- Value : this is the cross-elevation (deltaAz cosEL) pointing error (") if Az scan; the elevation error (") if an El scan;
or the focus correction (mm) if a Focus scan.
- Structural temperatures, "gbtts1_2003" etc: the correspondence between these sensor names and values used in the model
is given in Table 1 of PTCS project note 25 (see link above).
Full list of Column names
| 1 | ProjectID | project code : TPTCSxxx_yymmdd |
| 2 | ObsType | scan type, e.g., AzF, AzB, ElF, ElB, Focus |
| 3 | Type | ditto |
| 4 | Pol | polarization type, LCP or RCP |
| 5 | AstType | |
| 6 | Scan | scan number |
| 7 | MJDate | Modified Julian Date and fractional day |
| 8 | Source | source name |
| 9 | PointingModel | |
| 10 | J2000RA | J2000 Catalog position, in degrees |
| 11 | J2000Dec | |
| 12 | ObsFreq | Observing frequency in GHz |
| 13 | Obsc_Az | Observed place; refraction has been applied |
| 14 | Obsc_El | (degrees) |
| 15 | Mnt_Az | "Instrumental place", i.e., indicated encoder value |
| 16 | Mnt_El | (degrees) |
| 17 | Peak | Peak amplitude of scan, i.e, antenna Temp in Kelvin |
| 18 | PeakError | |
| 19 | Width | full width at half max of fitted gaussian, in arcsec |
| 20 | WidthError | |
| 21 | SNR | |
| 22 | Error | fit error (sigma) in "Value" |
| 23 | Value | The offset in arcsecond (Az or El) or in mm (Focus) |
| 24 | BaselineRMS | |
| 25 | AppRefModelVal | Value of refraction (degrees) applied to Obsc_El |
| 26 | NewRefModelVal | (no idea) |
| 27 | RefractError | |
| 28 | WindVel | median wind speed in m/s |
| 29 | WindDir |
| Structural temperatures (C) :
| location:
| 30 | gbtts1_2001 | Vertex tip
| 31 | gbtts1_2005 | Subreflector
| 32 | gbtts2_2001 | Backup structure (BUS) 15+440
| 33 | gbtts2_2002 | vertex right front
| 34 | gbtts2_2004 | vertex right rear
| 35 | gbtts3_2001 | vertex left front
| 36 | gbtts3_2002 | BUS 15-440
| 37 | gbtts3_2003 | vertex left rear
| 38 | gbtts3_2004 | horiz feedarm left
| 39 | gbtts4_2001 | horiz feedarm right
| 40 | gbtts4_2002 | right EL bearing
| 41 | gbtts4_2003 | left EL bearing
| 42 | gbtts4_2004 | BUS 25-200
| 43 | gbtts4_2005 | BUS 25+200
| 44 | gbtts4_2006 | BUS 25+000
| 45 | gbtts5_2001 | rt front alidade leg
| 46 | gbtts5_2002 | lft front alidade leg
| 47 | gbtts5_2003 | rt rear alidade leg
| 48 | gbtts5_2004 | lft rear alidade leg
| air temperatures (C) :
| 49 | at1 | air temp , (C) level 2
| 50 | at5 | air temp at subreflector
| 51 | at2 | air temp a quad detector
| 52 | at3 | air temp at vertex
| 53 | at4 | air temp below receiver room
| 54 | SR_XP | Subreflector X position (mm)
| 55 | SR_XPS |
| 56 | SR_YP | Subreflector Y position (mm)
| 57 | SR_YPS |
| 58 | SR_ZP | Subreflector Z position (mm)
| 59 | SR_ZPS |
| 60 | SR_XT | Subreflector X tilt
| 61 | SR_XTS |
| 62 | SR_YT | Subreflector Y tilt
| 63 | SR_YTS |
| 64 | SR_ZT | Subreflector Z tilt
| 65 | SR_ZTS |
| 66 | SMNTC_AZ | Az encoder command at scan midpoint
| 67 | SMNTC_EL | El encoder command at scan midpoint
| the "dT1Fdt" etc, are time derivatives of the structural temperatures :
| 68 | dT1Fdt |
| 69 | dT2Fdt |
| 70 | dT3Fdt |
| 71 | dT4Fdt |
| 72 | dT5Fdt |
| 73 | dT6Fdt |
| 74 | dT1Adt |
| 75 | dT2Adt |
| 76 | dT3Adt |
| 77 | dT4Adt |
| 78 | dT1Edt |
| 79 | dT2Edt |
| 80 | dT3Edt |
| 81 | dT4Edt |