SOFIE Signal Gain Analysis Mark Hervig GATS

# SOFIE Signal Gain Analysis Mark Hervig GATS

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## SOFIE Signal Gain Analysis Mark Hervig GATS

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1. SOFIE Signal Gain AnalysisMark HervigGATS

2. SOFIE Analog Signal Path Weak Channel Balance Attenuator attenuation = BAw A/D 14 bits -3V to 3V -213 to 213 counts 1 count = 366 V Vin,w Differential Amp gain = GV Strong Channel Balance Attenuator attenuation = BAs Vin,s • Vin is the signal into the balance attenuator, after synchronous rectification: • Vin = VA/Dmax * margin • set margin to 1.2, so Vin = 3V * 1.2 = 3.6V • we’ll get Vw and Vs below 3V using the BA’s • for example to get Vexo = 2.95V requires BA = 0.82 • The difference signal: • V = (Vin,w * BAw – Vin,s* BAs) * GV

3. Balance attenuator setting vs. V balance voltages • Difference signal balance voltage, Vbal: • Vbal = (Vin,w * BAw – Vin,s* BAs) * GV • Solve for BAw We can balance at various voltages to increase dynamic range in V Little impact on Vw These curves apply to all channels

4. V precision vs. V gain and balance attenuator settings count precision, CPV = (214 BAsGV)-1 These curves apply to all channels

5. V precision vs. balance attenuator setting Count precision, CPV = (214 BA)-1 Lowering BA reduces precision These curves apply to all channels

6. Recommended V Gain Settings Assumes 14 bit A/D, -3 to 3V. V balance voltage was –2.5V for all channels. Upper altitude is where the 1st 10 count change occurs. Lower altitude is where V reaches 0.8214 counts. Note that the CBE 1-count precisions are not CBE system noise. Required V precisions are taken as the strong band requirements. Signals were based on atmospheric transmissions calculated using a climatology for summer at 60°N. The analyses that lead to the above results are shown on the following pages.

7. SOFIE PC Radiometric Electronics Overview • Carrier Frequency = 1kHz, Modulation = 2 Hz, Effective Sync Rect Q = 500 • Nominal Equal System-wide Phasing: Butterworth and Bessel Filters

8. 1) O3 channel profiles Balance V at –2.5V BAs = 0.819 BAw = 0.613 GV = 3.3 V saturates at 60 km, or 0.8*214 counts

9. 1) O3 Channel useful altitude Useful altitude of V signals is determined by the V gain and balance attenuator settings. Baseline altitude range will be determined by GV Adjusting the BA settings changes the altitude range very little in this case

10. 2) SW particle channel profiles Balance V at –2.5V BAs = 0.819 BAw = 0.814 GV = 300 V useable through typical PMC

11. 3) H2O channel profiles Balance V at –2.5V BAs = 0.819 BAw = 0.812 GV = 96 V saturates at 50 km, or 0.8*214 counts

12. 3) H2O Channel useful altitude Useful altitude of V signals is determined by the V gain and balance attenuator settings. Baseline altitude range will be determined by GV We can adjust the BA settings to change our altitude range

13. 3) H2O channel useful altitude The V gain to saturate at 50 km altitude changes with V balance voltage Decreasing the V balance voltage increases the dynamic range With increased dynamic range, we can tolerate an increase in the V gain The figure shows the V gain that saturates V at 50 km vs. Vbal Decreasing Vbal allows us to get more precision and dynamic range

14. 4) 2.8 m CO2 channel profiles

15. 4) 2.8 m CO2 channel useful altitude Useful altitude of V signals is determined by the V gain and balance attenuator settings. Baseline altitude range will be determined by GV Adjusting the BA settings changes the altitude range

16. 5) IR particle channel profiles Balance V at –2.5V BAs = 0.819 BAw = 0.814 GV = 120 V useable through typical PMC

17. 6) CH4 channel profiles Balance V at –2.5V BAs = 0.819 BAw = 0.816 GV = 202 V saturates at 40 km, or 0.8*214 counts

18. 6) CH4 Channel useful altitude Useful altitude of V signals is determined by the V gain and balance attenuator settings. Baseline altitude range will be determined by GV Adjusting the BA settings changes the altitude range

19. 7) 4.3 m CO2 channel profiles

20. 7) 4.3 m CO2 channel useful altitude Useful altitude of V signals is determined by the V gain and balance attenuator settings. Baseline altitude range will be determined by GV Adjusting the BA settings changes the altitude range

21. 8) NO channel profiles Balance V at –2.5V BAs = 0.819 BAw = 0.817 GV = 300 V never saturates, but the signal is dominated by atmospheric interference below 80 km.