Presentation on theme: "Large Sky Dip Calibration Runs Taken once per Day. Lasts ~ 15 minutes long. Telescope elevation varies by 40 degrees. Calibrates the “Leakage” and relative."— Presentation transcript:
Large Sky Dip Calibration Runs Taken once per Day. Lasts ~ 15 minutes long. Telescope elevation varies by 40 degrees. Calibrates the “Leakage” and relative Total Power Gain between Diodes. Using atmospheric modeling, can calibrate the Absolute Total Power Gain of a Diode. Note that Mini sky Dips are taken in between CMB Patch Scans.
Sky Dip Calibration Q1 Total Power (mV) for Module 00 Phase switches off phase switches on time (5 second bins) Telescope Elevation (degrees)
Phase Switch Turned off Plotting only Phase Switch = ON Q1 Module 00 total power
Q1 Total Power versus Elevation More atmosphere Less atmosphere Our ADC has a “reversed” Proportionality. Need conversion from mV to Kelvin (aka “gain”). Gain is derived from “Sky temperature” model, and confirmed with TauA observations. Gains for each diode is stored in database. For Q1 module 00, gain ~ 2.6 mV/Kelvin 2 kelvin excursion in sky temperature
Atmospheric Contribution to Noise (tuned for QUIET)
ROUGH Calibration Assume* T(zenith) = 5 Kelvin Then T(sky temperature) = T(zenith)/sin(elevation) Then Gain = 2.9 mV/Kelvin * in reality, there is dependence on PWV and actual air temperature. Kelvin
Example: Estimate of Noise Temperature for Q1 Module 00 ADC (Phase switches Off) = 2300 mV ADC (85 degree elevation) = 2039 mV difference = 2300 – 2039 = 261 mV Gain (Q1 Module 00) = 2.9 mV/Kelvin Measured Power = 261/2.9 = 90 Kelvin CMB Noise Power = 3 K Atmospheric Noise Power ~ 5 K Noise seen at Diode ~ 90 – 3 – 5 = 82 Kelvin