PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 50 FILE_RECORDS = 305 ^SURF_HDR_TABLE = ("9073U00A.SRT",1) ^SURF_TABLE = ("9073U00A.SRT",6) INSTRUMENT_HOST_NAME = "MARS GLOBAL SURVEYOR" TARGET_NAME = "MARS" INSTRUMENT_NAME = "RADIO SCIENCE SUBSYSTEM" DATA_SET_ID = "MGS-M-RSS-5-SDP-V1.0" PRODUCT_ID = "9073U00A.SRT" PRODUCT_RELEASE_DATE = 2000-12-28 DESCRIPTION = "This file contains measurements of surface echoes obtained in the course of Mars Global Surveyor radio occultation observations. The time of geometric occultation and the sense of occultation (ingress or egress) were determined from high time resolution analysis of the carrier amplitude. A search was then made on either side of the carrier; if more power was found on one side, that was assumed to be from the echo. An estimate of the thermal noise background was obtained from the other side; that, in conjunction with an estimate of system temperature was used to calibrate the measurements. The table contains estimates of the peak frequency bin and the amplitude of both the carrier and the surface echo as a function of time. For more information on bistatic radar probing of planetary surfaces, see Simpson (IEEE Transactions on Geoscience and Remote Sensing, 31, 465-482, 1993)." START_TIME = 1999-03-14T20:00:01 STOP_TIME = 1999-03-14T20:07:00 SOFTWARE_NAME = "SURF2PDS;2000-06-26" PRODUCT_CREATION_TIME = 2000-06-27T03:21:37 PRODUCER_ID = "MGS RST" OBJECT = SURF_HDR_TABLE ROWS = 1 COLUMNS = 25 ROW_BYTES = 222 ROW_SUFFIX_BYTES = 28 INTERCHANGE_FORMAT = ASCII DESCRIPTION = "The SURF header contains ancillary data associated surface echo power measurements. Each header includes a single row of 25 data columns (222 total bytes), 26 ASCII blank characters to pad out the record, and an ASCII carriage-return line-feed pair at the end." OBJECT = COLUMN NAME = "START TIME" COLUMN_NUMBER = 1 DATA_TYPE = TIME START_BYTE = 1 BYTES = 19 UNIT = "N/A" DESCRIPTION = "The Earth Receive Time at which the first radio occultation data sample was acquired. The start time of the original ODR file. This is usually somewhat earlier than the first measurement reported in the data listing (SURF_TABLE) here." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "STOP TIME" COLUMN_NUMBER = 2 DATA_TYPE = TIME START_BYTE = 21 BYTES = 19 UNIT = "N/A" DESCRIPTION = "The Earth Receive Time at which the last radio occultation data sample was acquired. The stop time of the original ODR file. This is usually later than the last measurement reported in the data listing (SURF_TABLE) here." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "OCCULTATION TIME" COLUMN_NUMBER = 3 DATA_TYPE = ASCII_REAL START_BYTE = 41 BYTES = 12 FORMAT = "F12.6" UNIT = "SECOND" DESCRIPTION = "The Earth Receive Time when the geometrical ray path grazed the limb. At this point half of the Fresnel zone was presumably obscured, and received carrier power should have been one-fourth of its free space value. The time was computed using power versus time output from the POWERFIT program. Maximum and minimum carrier amplitudes within 3 seconds of the occultation established the amplitude range. For egress, the last sample below the 25 percent threshold served as a temporary marker. For ingress, working in time reverse order, a similar marker was found. The final occultation time was the time of the adjacent sample in the unocculted (free space) direction, usually with higher carrier power. Formal accuracy of this quantity is estimated to be +/-12.8 msec, the POWERFIT sample spacing. However, this method does not account for effects of the atmosphere at the limb; refraction is estimated to advance the occultation time by a few tenths of a second on egress and to delay it by a few tenths of a second on ingress." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "ORBIT NUMBER" COLUMN_NUMBER = 4 DATA_TYPE = ASCII_INTEGER START_BYTE = 54 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "Orbit number from which the data were acquired; set to zero if not known. NB: Orbit numbers were reset to 1 at the beginning of the MGS Mapping Phase (9 March 1999)." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "DSN ANTENNA NUMBER" COLUMN_NUMBER = 5 DATA_TYPE = ASCII_INTEGER START_BYTE = 60 BYTES = 2 FORMAT = "I2" UNIT = "N/A" DESCRIPTION = "Number of the DSN antenna used to collect the data (e.g., 14, 43, 65, ...)." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "OCCULTATION SENSE" COLUMN_NUMBER = 6 DATA_TYPE = CHARACTER START_BYTE = 64 BYTES = 1 FORMAT = "A1" UNIT = "N/A" DESCRIPTION = "The sense of the occultation: set to 'I' for ingress or to 'E' for egress." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "ODR FILE NAME" COLUMN_NUMBER = 7 DATA_TYPE = CHARACTER START_BYTE = 68 BYTES = 12 FORMAT = "A12" UNIT = "N/A" DESCRIPTION = "File name of the original open-loop data." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "FILTER FILE NAME" COLUMN_NUMBER = 8 DATA_TYPE = CHARACTER START_BYTE = 83 BYTES = 12 FORMAT = "A12" UNIT = "N/A" DESCRIPTION = "File name of the equalizing filter used to smooth the output spectrum." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "CARRIER TO NOISE RATIO" COLUMN_NUMBER = 9 DATA_TYPE = ASCII_REAL START_BYTE = 97 BYTES = 6 FORMAT = "F6.2" UNIT = "DECIBEL PER HERTZ" DESCRIPTION = "Estimate of unocculted carrier power to thermal noise power. Value is the highest found when computing (typically unaveraged) power spectra. An indication of relative data quality, but likely to be 3-6 dB higher than what would be obtained with averaging." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "SYSTEM TEMPERATURE" COLUMN_NUMBER = 10 DATA_TYPE = ASCII_REAL START_BYTE = 104 BYTES = 6 FORMAT = "F6.2" UNIT = "KELVIN" DESCRIPTION = "System temperature assumed in calibrating data to units of watts. This quantity is obtained in real time by the NASA Deep Space Network; usually measurements from two receivers are averaged. When no value appropriate for interpreting a given observation is available, the nominal value 30K is assumed." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "SAMPLE SPACING" COLUMN_NUMBER = 11 DATA_TYPE = ASCII_REAL START_BYTE = 111 BYTES = 8 FORMAT = "F8.6" UNIT = "SECOND" DESCRIPTION = "Time spacing of the complex samples used as input to this analysis. Spacing is twice the spacing of the original (real) samples." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "TRANSFORM LENGTH" COLUMN_NUMBER = 12 DATA_TYPE = ASCII_INTEGER START_BYTE = 120 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "Number of points in each power spectrum. Typically a number like 512." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "TIME PER SPECTRUM" COLUMN_NUMBER = 13 DATA_TYPE = ASCII_REAL START_BYTE = 126 BYTES = 8 FORMAT = "F8.6" UNIT = "SECOND" DESCRIPTION = "Time represented by each spectrum, and spacing between spectra. The product of the previous two columns multiplied by the number of spectra averaged." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "FREQUENCY RESOLUTION" COLUMN_NUMBER = 14 DATA_TYPE = ASCII_REAL START_BYTE = 135 BYTES = 7 FORMAT = "F7.4" UNIT = "HERTZ" DESCRIPTION = "Frequency resolution in each spectrum. TIME PER SPECTRUM multiplied by FREQUENCY RESOLUTION gives the number of spectra averaged incoherently." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "LOWEST NOISE BIN" COLUMN_NUMBER = 15 DATA_TYPE = ASCII_INTEGER START_BYTE = 143 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "Lowest frequency bin included in calculation of radio thermal noise background level. Total number of bins is given by TRANSFORM LENGTH. Noise bins should be on opposite side of carrier from surface echo." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "HIGHEST NOISE BIN" COLUMN_NUMBER = 16 DATA_TYPE = ASCII_INTEGER START_BYTE = 149 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "Highest frequency bin included in calculation of radio thermal noise background level. Total number of bins is given by TRANSFORM LENGTH. Noise bins should be on opposite side of carrier from surface echo." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "NUMBER OF NOISE POINTS" COLUMN_NUMBER = 17 DATA_TYPE = ASCII_INTEGER START_BYTE = 155 BYTES = 8 FORMAT = "I8" UNIT = "N/A" DESCRIPTION = "Number of noise values used to compute radio thermal noise background level. Number of frequency bins (from Columns 15 and 16) multiplied by the number of spectra gives this total." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "NOISE MEAN" COLUMN_NUMBER = 18 DATA_TYPE = ASCII_REAL START_BYTE = 164 BYTES = 10 FORMAT = "E10.4" UNIT = "N/A" DESCRIPTION = "Average of the noise measurements within the bounds defined by Columns 15-17." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "NOISE STANDARD DEVIATION" COLUMN_NUMBER = 19 DATA_TYPE = ASCII_REAL START_BYTE = 175 BYTES = 10 FORMAT = "E10.4" UNIT = "N/A" DESCRIPTION = "Standard deviation of the noise measurements within the bounds defined by Columns 15-17. For white noise and no spectral averaging Columns 18 and 19 should be very close." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "NUMBER OF MASKED FREQUENCY BINS" COLUMN_NUMBER = 20 DATA_TYPE = ASCII_INTEGER START_BYTE = 186 BYTES = 3 FORMAT = "I3" UNIT = "N/A" DESCRIPTION = "Number of frequency bins on each side of the carrier that were masked during search for and fit to the frequency track of the echo signal. If no masking were used, splatter from the carrier would dominate the search." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "FIRST TIME BIN IN FREQUENCY FIT" COLUMN_NUMBER = 21 DATA_TYPE = ASCII_INTEGER START_BYTE = 190 BYTES = 3 FORMAT = "I3" UNIT = "N/A" DESCRIPTION = "First time bin used in search for and fit to frequency track of the surface echo. Usually 41 for egress, variable for ingress." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "LAST TIME BIN IN FREQUENCY FIT" COLUMN_NUMBER = 22 DATA_TYPE = ASCII_INTEGER START_BYTE = 194 BYTES = 3 FORMAT = "I3" UNIT = "N/A" DESCRIPTION = "Last time bin used in search for and fit to frequency track of the surface echo. Usually 259 for ingress, variable for egress." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "ECHO FITTED SLOPE" COLUMN_NUMBER = 23 DATA_TYPE = ASCII_REAL START_BYTE = 198 BYTES = 11 FORMAT = "E11.4" UNIT = "HERTZ PER SECOND" DESCRIPTION = "Slope of the linear fit to surface echo position with respect to the carrier. This is the linear coefficient a in the equation f = a*t + b where f is frequency of surface echo relative to carrier t is time in seconds from the previous even hour b is constant coefficient (Column 24)." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "ECHO FITTED INTERCEPT" COLUMN_NUMBER = 24 DATA_TYPE = ASCII_REAL START_BYTE = 210 BYTES = 11 FORMAT = "E11.4" UNIT = "HERTZ" DESCRIPTION = "Intercept of the linear fit to echo position with respect to the carrier. This is the constant term b in the equation f = a*t + b where f is frequency of surface echo relative to carrier a is linear coefficient (Column 23) t is time in seconds from the previous even hour." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "FIT QUALITY FLAG" COLUMN_NUMBER = 25 DATA_TYPE = ASCII_INTEGER START_BYTE = 222 BYTES = 1 FORMAT = "I1" UNIT = "N/A" DESCRIPTION = "Integer indicating operator's evaluation of how well the fitted curve follows the echo. Default 1 = satisfactory 0 = unsatisfactory" END_OBJECT = COLUMN END_OBJECT = SURF_HDR_TABLE OBJECT = SURF_TABLE ROWS = 300 COLUMNS = 5 ROW_BYTES = 50 INTERCHANGE_FORMAT = ASCII DESCRIPTION = "Table contains time, bin numbers, and amplitudes of carrier and surface echo. Calculations were based on power spectra; typically 300 spectra were used, each having 512 frequency bins. Data are in five columns, delimited by ASCII commas (48 bytes total); the final two positions are occupied by an ASCII carriage-return and an ASCII line-feed." OBJECT = COLUMN NAME = "TIME" COLUMN_NUMBER = 1 DATA_TYPE = ASCII_REAL START_BYTE = 1 BYTES = 12 FORMAT = "F12.6" UNIT = "SECOND" DESCRIPTION = "Time at which the spectrum was calculated, in seconds from the previous ERT midnight." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "CARRIER BIN NUMBER" COLUMN_NUMBER = 2 DATA_TYPE = ASCII_INTEGER START_BYTE = 14 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "Number of the spectral bin with maximum power. This is presumed to be the carrier signal, and ordinarily would be near the center of the spectrum (a value of approximately 256 if TRANSFORM LENGTH is 512). Rarely, it could be strong interference from a ground source. During deep occultation, this value will be random." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "SURFACE ECHO BIN" COLUMN_NUMBER = 3 DATA_TYPE = ASCII_INTEGER START_BYTE = 20 BYTES = 5 FORMAT = "I5" UNIT = "N/A" DESCRIPTION = "Number of the spectral bin containing the presumed peak of the surface echo. After determination of occultation sense (ingress or egress) a search was made of the time-frequency space in which the surface echo should be found. Area within a few bins of the carrier was excluded. This is the location of whatever peak was found -- usually the surface echo when strong." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "CARRIER POWER" COLUMN_NUMBER = 4 DATA_TYPE = ASCII_REAL START_BYTE = 26 BYTES = 11 FORMAT = "E11.4" UNIT = "WATT" DESCRIPTION = "Carrier power in watts. Obtained by summing the power in the peak bin (CARRIER BIN NUMBER) plus three bins on either side, after removal of the noise baseline." END_OBJECT = COLUMN OBJECT = COLUMN NAME = "SURFACE ECHO POWER" COLUMN_NUMBER = 5 DATA_TYPE = ASCII_REAL START_BYTE = 38 BYTES = 11 FORMAT = "E11.4" UNIT = "WATT" DESCRIPTION = "Power in presumed surface echo. Obtained by (1) fitting a straight line to the echo offset frequency from the carrier [Column 3 - Column 2 multiplied by Hertz per bin; best fit is given by coefficients in Columns 23 and 24 of SURF_HDR_TABLE]; (2) summing powers in approximately 7 spectral bins centered on this line. This will be a poor estimate if the fit is not good." END_OBJECT = COLUMN END_OBJECT = SURF_TABLE END