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The Crossover Points files are distributed separately from the MGDRB but are described here for convenience.
Elements of the Crossover Files are generally characterized by the following items:
Definition Element definition.
Element type An element type can be bitfield or integer.
Storage type A storage type can be signed (signed integer), unsigned (unsigned integer), bit (contiguous sequence of bits) or character (contiguous sequence of ASCII characters).
Size Size of elements in 8-bit bytes.
Unit Unit of measure including scale factor, or none (/).
Minimum value Typical or approximate minimum element value.
Maximum value Typical or approximate maximum element value.
Nominal value Typical or approximate nominal element value.
Default value Element value when the measurement is not available or the element is not computable ("flag value").
Comment Other comment.
Due to the repetitive nature of the elements in this file, the separate ascending and descending parameters are given a single entry. For example, Dry_Corr_Asc and Dry_Corr_Des are both described in the entry below labeled "Dry_Corr_A/D". There are 6 parameters, all ending in "_Cro" which describe only the crossing point and hence, only occur once per record.
Att_Ptf_A/D
Definition Ptf-nadir angle estimated from platform elements. The off-nadir angle is the cone angle between altimeter electrical axis and nadir, nadir being defined as the normal to the reflecting surface.
Element type Integer
Storage type Unsigned
Size 1
Unit 0.01 degree
Minimum value 0
Maximum value 150
Default value 255
Comment See Att_Ptf MGDR parameter for details
Att_Wvf_A/D
Definition Off-nadir angle estimated from the measured waveform. The off-nadir angle is the cone angle between altimeter electrical axis and nadir, nadir being defined as the normal to the reflecting surface.
Element type Integer
Storage type Unsigned
Size 1
Unit 0.01 degree
Minimum value 0
Maximum value 150
Default value 255
Comment See Att_Ptf MGDR parameter for details
DR_SWH_Att_C_A/D
Definition Correction to altimeter tracker range for Significant Wave Height (SWH) and attitude effects at C band.
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -400
Maximum value 400
Default value 32767
Comment
DR_SWH_Att_K_A/D
Definition Correction to altimeter tracker range for Significant Wave Height (SWH) and attitude effects at Ku band.
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -400
Maximum value 400
Default value 32767
Comment
Dry_Corr_A/D
Definition Dry tropospheric correction interpolated at the altimeter measurement . time
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -3000
Maximum value -2000
Default value 32767
Comment This element corresponds to the dry tropospheric correction computation using respectively one of the 2 meteorological fields surrounding the altimeter measurement epoch (nearest value) and interpolating to measurement time. [See the Dry_Corr MGDR parameter for more details.]
Dry1_Corr_A/D
Definition Dry tropospheric correction before altimeter measurement .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -3000
Maximum value -2000
Default value 32767
Comment This element corresponds to the dry tropospheric correction computation using the first of the 2 meteorological fields surrounding the altimeter measurement epoch (nearest value). [See the Dry1_Corr MGDR parameter for more details.]
Dry2_Corr_A/D
Definition Dry tropospheric correction after altimeter measurement file).
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -3000
Maximum value -2000
Default value 32767
Comment This element corresponds to the dry tropospheric correction computation using the second of the 2 meteorological fields surrounding the altimeter measurement epoch (nearest value). [See the Dry2_Corr MGDR parameter for more details.]
Dry_Err_A/D
Definition Quality index on Dry_Corr
Element type Integer
Storage type Signed
Size 1
Unit /
Minimum value 0
Maximum value 9
Default value 127
Comment Its value ranges from 0 to 9 with lower ranges when this element is valuable and higher ranges when it is not valuable. The value is the larger of the two values describing the two meteorological fields.
Dry1_Err_A/D
Definition Quality index on Dry1_Corr
Element type Integer
Storage type Signed
Size 1
Unit /
Minimum value 0
Maximum value 9
Default value 127
Comment Its value ranges from 0 to 9 with lower ranges when this element is valuable and higher ranges when it is not valuable.
Dry2_Err_A/D
Definition Quality index on Dry2_Corr
Element type Integer
Storage type Signed
Size 1
Unit /
Minimum value 0
Maximum value 9
Default value 127
Comment Its value ranges from 0 to 9 with lower ranges when this element is valuable and higher ranges when it is not valuable.
EMB_Corr_K1_A/D
Definition Gaspar, Ku band range correction for electromagnetic bias (EMB)
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1200
Maximum value 0
Default value 32767
Comment This element is computed by linear interpolation from MGDR EMB values (EMB_Gaspar).
Geo_Bad_1_A/D
Definition Set of flags indicating ocean/land/ice states.
Element type Bitfield
Storage type Bit
Size 1
Unit /
Minimum value 0
Maximum value 255
Default value N/A
Comment
Geo_Bad_2_A/D
Definition Set of flags indicating the rain and tide conditions.
Element type Bitfield
Storage type Bit
Size 1
Unit /
Minimum value 0
Maximum value 255
Default value N/A
Comment
H_Alt_A/D
Definition Altimeter range .
Element type Integer
Storage type Signed
Size 4
Unit millimeter
Minimum value 120000000
Maximum value 140000000
Default value 2147483647
Comment This element is computed by spline interpolation from MGDR altimeter range values (H_Alt). Altimeter ranges are corrected for instrumental effects only.
H_EOT_CSR_A/D
Definition Height of the elastic ocean tide
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -15000
Maximum value 15000
Default value 32767
Comment This element is computed by linear interpolation from CSR 3.0 model MGDR elastic ocean tide values (H_EOT_CSR).
H_EOT_FES_A/D
Definition Height of the elastic ocean tide
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -15000
Maximum value 15000
Default value 32767
Comment This element is computed by linear interpolation from FES 95.2 model MGDR elastic ocean tide values (H_EOT_FES).
H_LT_A/D
Definition Ocean loading effect on tide
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1500
Maximum value 1500
Default value 32767
Comment This element is computed by linear interpolation from Cartwright and Ray model MGDR ocean loading effect values on tide (H_LT_C).
H_MSS_Cro
Definition Mean sea surface height above the reference ellipsoid at the measurement point.
Element type Integer
Storage type Signed
Size 4
Unit millimeter
Minimum value -300000
Maximum value 300000
Default value 2147483647
Comment This element is deduced from Rapp et al. mean sea surface height fields computed using Geos3, Seasat and Geosat altimeter data [Ref. 22].
H_Ocs_Cro
Definition Ocean depth at the measurement point.
Element type Integer
Storage type Signed
Size 2
Unit meter
Minimum value -15000
Maximum value 0
Default value 32767
Comment This element is computed from ETOPO5 database (NOAA,Boulder,Colorado)
H_Pol_A/D
Definition Geocentric pole tide height .
Element type Integer
Storage type Signed
Size 1
Unit millimeter
Minimum value -100
Maximum value 100
Default value 127
Comment This element is computed by linear interpolation from MGDR geocentric pole tide height values (H_Pol).
H_Set_A/D
Definition Height of the solid Earth tide .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 1000
Default value 32767
Comment This element is computed by linear interpolation from MGDR solid Earth tide height values (H_Set).
HP_Alt_A/D
Definition CNES altitude of satellite center of mass above the reference ellipsoid .
Element type Integer
Storage type Signed
Size 4
Unit millimeter
Minimum value 1200000000
Maximum value 1400000000
Default value 2147483647
Comment This element is computed by linear interpolation from MGDR CNES altitude values (HP_Sat).
INV_BAR_A/D
Definition Inverse barometric effect correction
Element type Integer
Storage type Signed
Size 2
Unit mm
Minimum value -1300
Maximum value 3105
Default value 32 767
Comment INV_BAR has to be added to instrument range to correct for the static inverse barometric effect. Note: this correction is not always valid - see 4.6.
Iono_Ben_A/D
Definition Ionospheric correction issued from Bent model .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 0
Default value 32767
Comment This element is computed by linear interpolation from MGDR Bent ionospheric correction values (Iono_Ben).
Iono_Cor_A/D
Definition TOPEX dual-frequency ionospheric correction .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -500
Maximum value 40
Default value 32767
Comment This element is computed by linear interpolation from MGDR TOPEX dual-frequency ionospheric correction values (Iono_Cor).
Iono_Dor_A/D
Definition DORIS ionospheric correction .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 0
Default value 32767
Comment This element is computed by linear interpolation from MGDR DORIS ionospheric correction values (Iono_Dor).
Iono_Dor_Bad_A/D
Definition Quality index on Iono_Dor
Element type Integer
Storage type Signed
Size 1
Unit /
Minimum value 0
Maximum value 9
Default value 127
Comment Its value ranges from 0 to 9 with lower ranges when this element is valuable and higher ranges when it is not valuable.
Lat_Cro
Definition Geodetic latitude of the crossover points.
Element type Integer
Storage type Signed
Size 4
Unit microdegree
Minimum value -90000000
Maximum value 90000000
Default value N/A
Comment This element is computed by linear interpolation from MGDR geodetic latitude values (Lat_Tra).
Lon_Cro
Definition Geodetic latitude of the crossover points.
Element type Integer
Storage type Signed
Size 4
Unit microdegree
Minimum value 0
Maximum value 360000000
Default value N/A
Comment This element is computed by linear interpolation from MGDR geodetic longitude values (Lon_Tra).
Net_Instr_R_Corr_C_A/D
Definition C band, net (summed) instrument correction to range.
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -5000
Maximum value 2000
Default value 32767
Comment See Net_Instr_R_Corr_C for more details.
Net_Instr_R_Corr_K_A/D
Definition Ku band, net (summed) instrument correction to range.
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -5000
Maximum value 0
Default value N/A
Comment See Net_Instr_R_Corr_K for more details.
Num_Pas_A/D
Definition Pass-file number of the ascending pass-file from which the ascending crossover point is issued.
Element type Integer
Storage type Unsigned
Size 1
Unit counts
Minimum value 1
Maximum value 254
Default value N/A
Comment /
Range_Deriv_A/D
Definition One per second range derivative.
Element type Integer
Storage type Signed
Size 2
Unit centimeter per second
Minimum value -3500
Maximum value 3500
Default value 32767
Comment See Range_Deriv MGDR for more details
RMS_H_Alt
Definition Root Mean Square (RMS) of H_Alt_SME(i) about the fit or average used to obtain the one per frame value (H_Alt).
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value 0
Maximum value 10000
Default value 32767
Comment /
Sat_Alt_A/D
Definition NASA altitude of satellite center of mass above the reference ellipsoid .
Element type Integer
Storage type Signed
Size 4
Unit millimeter
Minimum value 1200000000
Maximum value 1400000000
Default value 2147483647
Comment This element is computed by linear interpolation from MGDR NASA altitude values (Sat_Alt).
Sigma0_C_A/D
Definition C band, backscatter coefficient computed from AGC_C.
Element type Integer
Storage type Unsigned
Size 2
Unit 0.01 decibel
Minimum value 0
Maximum value 32767
Default value 65535
Comment /
Sigma0_K_A/D
Definition Ku band, backscatter coefficient computed from AGC_K.
Element type Integer
Storage type Unsigned
Size 2
Unit 0.01 decibel
Minimum value 0
Maximum value 3 000
Default value 65 535
Comment /
Spares_Cro
Definition Spares for additional crossing point information
Element type Integer
Storage type Byte
Size 8
Unit /
Minimum value N/A
Maximum value N/S
Default value 0
Comment Some or all of these bytes this may be used for parameters in future versions of this product
Spares_A/D
Definition Spares for additional crossing point information
Element type Integer
Storage type Byte
Size 45
Unit /
Minimum value N/A
Maximum value N/S
Default value 0
Comment Some or all of these bytes this may be used for parameters in future versions of this product. There are separate "spare" fields, each 45 bytes, for ascending and descending data.
Spline_RMS_A/D
Definition Root Mean Square (RMS) of the 8 distances between the satellite and the sea surface about the spline used to get H_Alt_A/D through interpolation.
Element type Integer
Storage type Signed
Size 1
Unit millimeter
Minimum value 0
Maximum value 80
Default value 127
Comment /
SWH_C_A/D
Definition Significant Wave Height (SWH), C band.
Element type Integer
Storage type Unsigned
Size 2
Unit 0.01 meter
Minimum value 0
Maximum value 32767
Default value 65535
Comment This element is computed by linear interpolation from MGDR Significant Wave Height values (SWH_C).
SWH_K_A/D
Definition Significant Wave Height (SWH), Ku band.
Element type Integer
Storage type Unsigned
Size 1
Unit 0.01 meter
Minimum value 0
Maximum value 32727
Default value 65535
Comment This element is computed by linear interpolation from MGDR Significant Wave Height values (SWH_K).
Tim_Moy_A/D_1
Definition Time elapsed between the reference epoch1 and the ascending crossover point, day part.
Element type Integer
Storage type Signed
Size 2
Unit day
Minimum value /
Maximum value /
Default value N/A
Comment This element is computed by spline interpolation from MGDR elapsed time values (Tim_Moy_1, Tim_Moy_2, Tim_Moy_3). The complete elapsed time (days, milliseconds and micro- seconds) which corresponds to the time when the satellite passes ascending over the crossover point location, can be obtained, with respect to unit systems, as follows:
Elapsed Time = Tim_Moy_A/D_1 + Tim_Moy_A/D_2 + Tim_Moy_A/D_3
Tim_Moy_A/D_2
Definition Number of milliseconds in the day for the complete elapsed time (see Tim_Moy_A/D_1 and Tim_Moy_A/D_3).
Element type Integer
Storage type Signed
Size 4
Unit millisecond
Minimum value /
Maximum value /
Default value N/A
Comment This element is computed by spline interpolation from MGDR elapsed time values (Tim_Moy_1, Tim_Moy_2, Tim_Moy_3). It includes "UTC leap second".
Tim_Moy_A/D_3
Definition Number of microseconds in the milliseconds for the complete elapsed time .
Element type Integer
Storage type Signed
Size 2
Unit microsecond
Minimum value /
Maximum value /
Default value N/A
Comment This element is computed by spline interpolation from MGDR elapsed time values (Tim_Moy_1, Tim_Moy_2, Tim_Moy_3).
Typ_Cro
Definition Type of the crossover points.
Element type Integer
Storage type Signed
Size 1
Unit N/A
Minimum value 0
Maximum value 3
Default value none
Comment Values are:
0 for TOPEX/TOPEX crossovers type (T/T),
1 for POSEIDON/POSEIDON crossovers type (P/P),
2 for TOPEX/POSEIDON crossovers type (T/P),
3 for POSEIDON/TOPEX crossovers type (P/T).
Wet_Corr_A/D
Definition Wet tropospheric correction interpolated at the altimeter measurement time.
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 0
Default value 32767
Comment This element corresponds to the wet tropospheric correction computation obtained from models of water vapor from the French Meteorological Office via the surface meteorological data file and interpolating at the measurement time. [See the Wet_Corr MGDR parameter for more details].
Wet_H_Err_A/D
Definition Quality index on Wet_Corr.
Element type Integer
Storage type Signed
Size 1
Unit /
Minimum value 0
Maximum value 9
Default value 127
Comment Its value ranges from 0 to 9 with lower ranges when this element is valuable and higher ranges when it is not valuable.
Wet_H_Rad_A/D
Definition Radiometer wet tropospheric .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 0
Default value 32767
Comment This element is computed by linear interpolation from MGDR radiometer wet tropospheric correction values (Wet_H_Rad).
Wet1_Corr_A/D
Definition Wet tropospheric correction before altimeter measurement .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 0
Default value 32767
Comment This element corresponds to the wet tropospheric correction computation obtained from models of water vapor from the French Meteorological Office via the surface meteorological data file. [See the Wet1_Corr MGDR parameter for more details].
Wet2_Corr_A/D
Definition Wet tropospheric correction after altimeter measurement .
Element type Integer
Storage type Signed
Size 2
Unit millimeter
Minimum value -1000
Maximum value 0
Default value 32767
Comment This element corresponds to the wet tropospheric correction computation obtained from models of water vapor from the French Meteorological Office via the surface meteorological data file. [See the Wet1_Corr MGDR parameter for more details].
Wind_Sp_A/D
Definition Wind intensity .
Element type Integer
Storage type Unsigned
Size 1
Unit 0.1 meter per second
Minimum value 0
Maximum value 250
Default value 255
Comment This element is computed by linear interpolation from MGDR wind speed values (Wind_Sp).
