Current GBT Performance

1
Current GBT Performance
2
Systematic Focus Errors
Axial Focus Offset air temperature versus
elevation
3
Gravitational Temperature Focus Effects
Temperature Effect
Gravitational Effect
Measure focus over short time period
NCP source 01178928
4
Systematic Pointing Errors
5
Plan of Attack

• Rationalize data acquisition
• Rationalize data analysis
• Implement temperature sensor system
• Concentrate efforts on pointing and focus
• Characterize performance with X-band (8 -10 GHz)

6
Data Quality
Gaussian Fits (Az, El, Focus) Polarization (LCP
RCP) Direction (Forward Backward)
Jack Scan
7
Data Quality Pointing (LCP RCP)
8
Data Quality Pointing (LCP RCP)
Flux (9 GHz) gt 0.08 Jy RMS lt 2.5 arcsec lt 0.03
HPBW
9
Data Quality Focus (LCP RCP)
Flux (9 GHz) gt 0.08 Jy RMS lt 3.8 mm ltlt focus
beamwidth
10
Data Quality Pointing (F B)
11
Data Quality Wind
12
Observational Strategy

• NCP source to probe temperature effects
• Up-down sources at night to probe gravity effects
• All-sky for a combination

13
Initial Results

• All-sky (Az, El) pointing
• Removed systematic pointing residuals
• Simultaneous fits to gravity and temperature
• Separate two effects
• Refine focus and pointing models

14
Current Performance

• Model
• Simultaneous solution to temperature and gravity
  effects
• Datasets
• All-sky pointing run (2003 Nov 20)
• Half-power tracking (2003 Nov 20)
• Metrics
• Blind pointing
• Offset pointing
• Continuous Tracking

15
Blind Pointing Azimuth
16
Blind Pointing Elevation
17
Blind Focus
18
Offset Pointing Azimuth and Elevation
19
Offset Focus
20
Tracking Ku-band (14 GHz) El half-power track
21
Current Performance (NO temperature corrections)
Benign Conditions (1) Exclude 1000 ? 1800
(2) Wind lt 2.5 m/s
Blind Pointing (1 point/focus) Offset
Pointing (90 min) Continuous Tracking
(30 min)
22
Supplemental Material
23
Blind Focus
24
Blind Pointing residuals versus (A, Z)
25
Blind Pointing residuals versus time
26
Blind Pointing 2-D RMS
Raw Residuals
One PEAK at the start of the evening
27
Blind Pointing Azimuth
28
Blind Pointing Elevation
29
Blind Focus
30
Tracking Ku-band (14 GHz) El half-power track
31
Tracking Ku-band (14 GHz) El half-power track