PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 1998-03-15 NOTE = "Internal memo describing how DSS 14 system temperature and gain corrections were derived from calibrations and data during analysis of the Clementine bistatic radar experiment." END_OBJECT = TEXT END Amplitude Calibration of DSS 14 data on 94/099 ============================================== Definitions =========== Data Path for Processing ------------------------ Channel 1 is S-RCP, Channel 3 is S-LCP. ODR Original data (on tape) | V -------- | PREPMO | Parse by channel, store in separate files -------- | PREPLOOK (power spectra plots) and V PREPOWER (average sample power vs time *.1P{1,3} plots) used to find times at which signal | levels changed. V --------- | PREPFND |<-- FL14S{R,L}01.SPC Filter and decimate (1:1) with separate --------- equalizing filter for each channel. | Filters based on power spectra averaged V over 19:56:47 (71807 sec) to 20:01:51 *.PF{1,3} (72111 sec). | | --------- |--> | FND | Look at low-side window (bins 201-328 of | | (8,201) |-> *.F1{1,3} 1024) to monitor time variability of noise | --------- power (absence of carrier, surface echo) | | --------- |--> | FND | Look at high-side window (bins 701-828 of | | (8,701) |-> *.F4{1,3} 1024) to monitor time variability of noise | --------- power (absence of carrier, surface echo) V ------ Compensate for attenuator changes, | GAIN | spontaneous maser/amplifier gain ------ changes | V *.GN{1,3} | --------- |-->| FND | Look at low-side noise window after gain | | (8,201) |-> *.F2{1,3} correction; carrier moves into window at | --------- end of run. V --------- | FND | Use high-side window (bins 701-828 of | (8,701) |-> *.F3{1,3} 1024) for tape-tape amplitude calibration. --------- Terms ----- Tsys Effective noise temperature of receiver electronics (expect channels to be different) Tsky Effective noise temperature of dark sky (should be same on both channels, includes unknown reflector and feed contributions; during tracking of lunar limb, may also include solar component; assumed near 3K, but that may be too low) Tctr Effective noise temperature of center of Moon (may be slightly higher at full Moon; should be same on both channels; includes unknown reflector and feed contributions) Tlim Effective noise temperature of lunar limb plus sky back- ground when DSS is tracking north/south pole target (should be roughly half of Tctr; found to be different on each channel because of 'squinting' in feed; includes unknown reflector and feed contri- butions; may include partial solar contribution) Tamb Ambient load temperature Able to Measure --------------- Tsys + Tsky Point antenna at zenith Tsys + Tamb Connect receiving system to ambient load Tsys + Tctr Point antenna at center of Moon Tsys + Tlim Point antenna at polar target region Local temperature was reported toward the end of the run; that is taken to be the ambient load temperature throughout. Unfortunately we didn't ask explicitly for the temperature of the ambient load. Local time of the observations was 10:48 AM to 01:05 PM. Tamb = 58F = 287.44K (1) Y-Factor Definitions -------------------- Tsys + Tamb Y1 = ----------- (2) Tsys + Tsky Tsys + Tamb Y2 = ----------- (3) Tsys + Tctr Tsys + Tamb Y3 = ----------- (4) Tsys + Tlim Adjustments =========== Attenuator changes which can be verified by their signal characteristics (one signal level followed by up to 10 msec of no signal followed by a second signal level offset by an integral number of dB) and/or in the ODR header have been corrected in the GAIN program so that an effectively constant attenuator setting is maintained on each channel. The noise power on Channel 1, based on ambient load measurements is about 6.5 percent higher than the noise power on Channel 3. The reference above has been adjusted to reflect this difference. It was observed at several points that attenuator setting changes between 39 and 40 dB on Channel 1 resulted in 0.8 dB of signal/noise level change. This is presumably because a combination of 1, 8, 10, and 20 dB attenuators at 39 dB is swapped for a single 40 dB attenuator at that transition. Hence, all attenuator changes crossing the 39-40 dB boundary (to/from the low 40's) are assumed to be integral dB's less 0.2 dB. Signal/noise level changes of up to 0.7 dB were observed on Channel 3 between about 18:45 and 19:25. No corresponding changes were seen on Channel 1. These are assumed to have been spontaneous gain changes in the maser and/or amplifiers on the LCP side -- that did not affect SNR. They have been removed empirically by the GAIN program; details are below. Empirical Gain Corrections ========================== At 67559 sec on 94/099 there was an anomalous gain change on CH3. The total power and the power in noise windows above and below the signal/echo in the passband decreased by about 0.7 dB over a little less than 1 sec. Between 68458 and 68915 sec the signal increased by about 0.3 dB; the rise and decay occurred over many seconds and the 0.3 dB change was only approximate -- the level was not constant. Between 69014 and 69885 the signal (and noise) level changed several times, ending at a level very nearly the same as before 67559. We assume these are instabilities in the maser or some other amplifier circuit. Since both the signal and noise went up/down by approximately the same amounts, we conclude that there were no changes in configuration. Since only CH3 was affected, we conclude that these changes were not the result of ground antenna pointing errors, intercession of clouds, or other natural path changes. We have corrected the gain during these times empirically, using linear approximations. Measurements ============ Ambient Load and Other Calibrations ----------------------------------- Measurements are summarized in Table 1 for 20 time intervals on RCP (R01 through R20) and 22 time intervals on LCP (L01 through L22). Intervals are not contiguous because of allowances for settling time after attenuator changes, tape boundaries, instabilities in LCP gain, and front-end overloads when the HGA was pointed toward Earth. Targets were: SKY = dark sky AMB = ambient load LIM = South Pole and lunar limb CTR = center of Moon Individual measurements were 1 second averages of FNDPOWER output from the *.F4{1,3} files (see above). These were averaged over the intervals shown in Table 1 and the standard deviations of the 1-sec points were calculated (column 7). The mean (column 7) was scaled by the effective attenuator setting (column 6) to obtain the adjusted mean in column 8. Values from the same 'target' in adjacent intervals were weighted and averaged to give the final value in column 9. Numbers in parentheses indicate the intervals in the average (if more than one). (1) R02 and R03 (2) R04 through R15 (3) R16 and R17 (4) R18 and R19 (5) L02 and L03 (6) L04 through L18 (7) L20 and L21 Values in column 9 were used in equations (2)-(4) to find Tsys, Tctr, and Tlim. Those results are shown in Table 2. ---------------------------------------------------------------------------- Table 1. Amplitude Calibration Measurements ---------------------------------------------------------------------------- No Tgt Start Stop Nbr Attnr Mean+/-Std Dev Adj Weighted (sec) (sec) of (dB) Measured Noise Mean Average Pts Power (linear) (linear) (linear) --- --- ----- ----- --- ----- --------------------- -------- -------- R01 SKY 64150 64675 526 30.00 4.455e-03+/-8.101e-05 4.455 4.455 R02 AMB 64695 64745 51 39.80 6.679e-03+/-1.333e-04 63.785 63.606(1) R03 AMB 64760 64875 116 40.80 5.284e-03+/-9.526e-05 63.528 R04 LIM 65562 65612 51 39.80 1.735e-03+/-3.426e-05 16.568 R05 LIM 65614 65790 177 35.00 5.079e-03+/-1.011e-04 16.061 R06 LIM 65793 65887 95 39.80 1.737e-03+/-3.332e-05 16.592 R07 LIM 65891 66045 155 38.00 2.547e-03+/-5.492e-05 16.072 R08 LIM 66046 67005 960 38.00 2.521e-03+/-5.824e-05 15.905 R09 LIM 67006 67235 230 38.00 2.475e-03+/-4.463e-05 15.618 16.014(2) R10 LIM 67239 67557 319 39.00 1.940e-03+/-4.515e-05 15.414 R11 LIM 67561 67965 405 39.80 1.676e-03+/-3.670e-05 16.010 R12 LIM 67966 68925 960 39.80 1.671e-03+/-3.855e-05 15.959 R13 LIM 68926 69885 960 39.80 1.660e-03+/-3.777e-05 15.851 R14 LIM 69886 70845 960 39.80 1.701e-03+/-3.573e-05 16.249 R15 LIM 70846 71460 615 39.80 1.723e-03+/-3.675e-05 16.456 R16 CTR 71489 71522 34 35.00 1.301e-02+/-3.014e-04 41.138 42.330(3) R17 CTR 71525 71700 176 39.80 4.457e-03+/-8.637e-05 42.560 R18 AMB 71745 71805 61 39.80 6.352e-03+/-9.985e-05 60.664 60.298(4) R19 AMB 71815 72105 291 40.80 5.009e-03+/-9.075e-05 60.221 R20 SKY 72125 72309 185 30.00 4.212e-03+/-7.620e-05 4.212 4.212 L01 SKY 64175 64675 501 30.00 2.202e-03+/-4.098e-05 2.202 2.202 L02 AMB 64685 64765 81 40.00 3.337e-03+/-8.062e-05 33.373 33.436(5) L03 AMB 64770 64870 101 41.00 2.660e-03+/-6.021e-05 33.486 L04 LIM 65571 65605 35 40.00 9.865e-04+/-2.184e-05 9.865 L05 LIM 65607 65815 209 35.00 3.078e-03+/-6.549e-05 9.733 L06 LIM 65819 65885 67 40.00 9.781e-04+/-1.846e-05 9.781 L07 LIM 65888 66045 158 38.00 1.522e-03+/-3.029e-05 9.602 L08 LIM 66046 67005 960 38.00 1.513e-03+/-3.376e-05 9.545 L09 LIM 67006 67239 234 38.00 1.507e-03+/-2.905e-05 9.505 L10 LIM 67243 67290 48 39.00 1.175e-03+/-2.518e-05 9.332 L11 LIM 67292 67350 59 40.00 9.465e-04+/-2.017e-05 9.465 9.543(6) L12 LIM 67353 67552 200 41.00 7.639e-04+/-1.921e-05 9.617 L13 LIM 67555 67558 4 42.00 6.247e-04+/-8.386e-06 9.900 L14 LIM 67565 67965 401 42.70 5.253e-04+/-1.113e-05 9.782 L15 LIM 67966 68445 480 42.70 5.193e-04+/-1.177e-05 9.669 L16 LIM 68926 68935 10 42.70 5.229e-04+/-9.387e-06 9.736 L17 LIM 69886 70845 960 42.00 5.922e-04+/-1.269e-05 9.386 L18 LIM 70846 71460 615 42.00 5.942e-04+/-1.282e-05 9.417 L19 CTR 71610 71710 101 35.00 6.896e-03+/-1.441e-04 21.808 21.808 L20 AMB 71745 71800 56 35.00 9.889e-03+/-1.854e-04 31.273 31.488(7) L21 AMB 71806 72105 300 41.00 2.504e-03+/-4.567e-05 31.528 L22 SKY 72125 72309 185 30.00 2.083e-03+/-3.885e-05 2.083 2.083 ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Table 2. Equivalent Noise Temperatures from Calibration Measurements ---------------------------------------------------------------------------- Right Circular (RCP) Polarization Tsky (K) Tsys (K) Tsys (K) Tctr (K) Tlim (K) (64150-64875 s) (71745-72309 s) (71489-72105 s) (65562-72105 s) (Y1=14.28) (Y1=14.32) (Y2=1.424) (Y3=3.765) -------- --------------- --------------- --------------- --------------- 0 21.65 21.59 195.35 59.06 1 20.57 20.51 195.67 59.86 3 18.42 18.36 196.31 61.45 5 16.27 16.21 196.96 63.40 Left Circular (LCP) Polarization Tsky (K) Tsys (K) Tsys (K) Tctr (K) Tlim (K) (64150-64875 s) (71745-72309 s) (71610-72105 s) (65571-72105 s) (Y1=15.18) (Y1=15.12) (Y2=1.444) (Y3=3.300) -------- --------------- --------------- --------------- --------------- 0 20.26 20.36 192.82 72.92 1 19.19 19.29 193.15 73.67 3 17.05 17.15 193.81 75.16 5 14.91 15.01 194.47 76.66 ---------------------------------------------------------------------------- The Tsys values from pre-cal and post-cal are extremely close (<1%) on both polarizations. This is good news for calibrations of signal levels versus cosmic noise background. On the other hand, the measured LEVELS with dark sky as the target are about 5.7% higher during pre-cal for both RCP and LCP compared with post-cal. This suggests that system gain (maser?) may vary by a few percent over several hours. That's not unreasonable, but it seems unlikely that BOTH masers would vary by the same amount. In any case, the long term system gain should be good at the 5.7% level (1.2K). The ~13.5K (20.1%) difference between the Tlim values on CH1 and CH3 may come from different 'squint' in the two polarizations. Mike Wert at JPL estimates the squint to be about 0.02 deg for the 70-m antennas at S-band. This translates to about 18.5 percent of the S-band beamwidth -- a little larger than our measured difference, but perhaps OK if all of the squint were in elevation. For observations of the lunar South Pole near transit, an elevation error should be perpendicular to the limb. In other measurements in which the antenna sidelobes might not be so important (Tctr, for example) the two are much closer. Tape to Tape Checks ------------------- Comparison of noise levels at boundaries between tapes is as follows. These values were taken from *.F2{1,3} for Low-Side Matching and from *.F3{1,3} files for High-Side Matching -- in both cases, after gain correction. Low-Side Matching High-Side Matching (bins 201-328; dB) (bins 701-828; dB) CH1 CH3 CH1 CH3 ---------------+--------------+------------+------------+------------+ start | | | -26.51 | -26.82 | 40991748-------+--------------+------------+------------+------------+ end | -2.20 | -16.23 | -2.27 | -16.24 | ---------------+--------------+------------+------------+------------+ start | -2.4 | -16. | -2.38 | -16.25 | 40991804-------+--------------+------------+------------+------------+ end | -20.9 | -20.4 | -20.89 | -20.38 | ---------------+--------------+------------+------------+------------+ start | -20.9 | -20.4 | -21. | -20.5 | 40991820-------+--------------+------------+------------+------------+ end | -21.0 | -20.4 | -21.1 | -20.4 | ---------------+--------------+------------+------------+------------+ start | -21.0 | -20.4 | -21.1 | -20.5 | 40991836-------+--------------+------------+------------+------------+ end | -21.0 | -20.3 | -21.0 | -20.4 | ---------------+--------------+------------+------------+------------+ start | -21.0 | -20.3 | -21.0 | -20.4 | 40991852-------+--------------+------------+------------+------------+ end | -20.9 | -20.3 | -20.9 | -20.4 | ---------------+--------------+------------+------------+------------+ start | | | -21.0 | -20.35 | 40991908-------+--------------+------------+------------+------------+ end | | | -20.9 | -20.55 | ---------------+--------------+------------+------------+------------+ start | | | -20.9 | -20.5 | 40991924-------+--------------+------------+------------+------------+ end | | | -20.9 | -20.5 | ---------------+--------------+------------+------------+------------+ start | -20.8 | -20.50 | -20.8 | -20.5 | 40991940-------+--------------+------------+------------+------------+ end | -15.18 | -15.28 | -15.17 | -15.3 | ---------------+--------------+------------+------------+------------+ Dick Simpson 13 October 1997 editorial improvements: 15 Jan 1998 largely rewritten: 13 March 1998