NOAA KLM User's Guide
The following subsections describe the contents of the 1b data set:
Each major frame (32 seconds) of raw SBUV/2 data received from the satellite results in one discrete or two sweep data records on the 1b data set. Each discrete data record contains SBUV/2 instrument data collected from 12 discrete wavelengths by the monochromator (one wavelength if it is in the position mode) and one wavelength by the CCR plus electronic calibration data. The instrument may be in discrete, sweep, position, wavelength calibration or diffuser decontamination mode and viewing either the Earth, wavelength calibration lamp or diffuser plate. Each sweep data record contains SBUV/2 instrument data collected in the instrument sweep mode. In this mode the instrument will usually be viewing the diffuser plate in order to take solar measurements, however other viewing scenes are possible. For a complete set of 1680 wavelength measurements, twelve 16 second sweep data records are required. These correspond to six 32 second major frames.
All SBUV/2 data are preserved as raw counts on the 1b data set. The only conversions to engineering units are done for the orbital and daily statistics.
The data on the 1b data set are arranged in terms of SBUV/2 orbits. The SBUV/2 orbit definition is different from the standard TIROS-N series (NOAA/NESDIS) orbit definition. Each SBUV/2 orbit begins when the center of the SBUV/2 instrument field of view (FOV) transits the equator on the dark viewing side of the Earth and continues through one satellite revolution about the Earth. Earth location data is used to ascertain equator crossing but is only given for the start time of each TIP major frame's worth of data. Thus, the SBUV/2 orbital designation of each TIP major frame's worth of information is based on the earth location at the start of each major frame.
The orbit definition used on the TIROS-N series satellite have the orbital boundary occurring at northbound equator crossing regardless of the time the satellite views the Earth. By this definition an afternoon satellite's (northbound equator crossing on the sunlit side of the Earth) orbits begin during daylight viewing times (i.e. about 50 minutes out of phase with SBUV/2 orbits). SBUV/2 will fly only on afternoon satellites. The change in the orbit definition is to provide continuity with that used for Nimbus-7 SBUV.
Each major frame contains 32 channels, or groups of 10 minor frames, with each channel containing one second's worth of data. Some of the data stored in a particular channel is data that was actually sampled during the previous second and thus belongs to the previous channel. Data items belonging to the previous channel are synchronized (placed in the proper channel) before being written to the daily 1b data set on either discrete sweep data records. This means that some of the data arriving in the first channel of a given major frame is placed in the last channel of the previous major frame before being processed.
The following items need synchronization.
Meteorological data is provided to the SBUV/2 Data Set from the TIROS Operational Vertical Sounder (TOVS) carried aboard the same satellite as the SBUV/2 instrument. The total ozone algorithm requires cloud information primarily to estimate the ozone hidden from the satellite sensor below the clouds. The TOVS utilizes three instruments for the satellites prior to NOAA-K:
1) A High Resolution Infrared Radiometric Sounder (HIRS/2),
2) A Microwave Sounding Unit (MSU), and
3) A Stratospheric Sounding Unit (SSU).
The TOVS products used by SBUV/2 are: cloud amounts, cloud top temperatures, and vertical profiles of atmospheric temperatures.
The vertical temperature profiles are given for up to forty specified pressure levels ranging from 1000 mb (or surface level) to 0.1 mb. These profiles represent one "box" in the current operational TOVS processing system (formerly a "box" in the old TOVS processing system). A "minibox" consists of 63 HIRS/2 fields of view (called spots) from 7 HIRS/2 scan lines (a "box"consisted of 9 spots from 3 scan lines). Certain quality checks are made during TOVS processing to assure the reasonableness of the temperature profiles. If any of these checks indicate a bad sounding, the profile is rejected during the SBUV/2 processing and replaced with fill values.
Cloud amounts and cloud top temperatures are provided on a spot by spot basis. The current operational TOVS processing system provides SBUV/2 with cloud data for boxes which are adjacent to nadir. Miniboxes are constructed by selection of the appropriate spots in a box. Cloud top pressures (analogous to cloud top height) are computed for each spot by linear interpolation of the cloud top temperature between adjacent levels in the temperature profile.
Averages of cloud amount, cloud top temperature, and atmospheric temperature profiles are computed to represent the area sampled by those SBUV/2 fields of view (the four longest wavelengths fields of view in the discrete mode) used in the total ozone computation. This area is equivalent to 30 HIRS/2 spots. Cloud averages are computed using all spots (except fills) lying within the composite SBUV/2 field of view area. Temperature profile averages include only those from miniboxes with two or three HIRS/2 scan lines lying within this composite SBUV/2 field of view area.
Temperatures of 20 pressure levels (more than needed by the ozone algorithms) have been saved on the 1b Data Set for future implementation of temperature dependency of the ozone absorption coefficients.
Meteorological data is collected only when the instrument is in the discrete mode (normal mode for ozone determination), the position mode (rarely if ever used), and wavelength calibration mode. These three modes have in common the same record format, i.e. the discrete data record. As the ancillary data is not time dependent, this data will be written once for each Daily 1b data set. It is not saved for sweep mode data.
The source of this data is the same as that used for Nimbus SBUV processing. It was originally derived from a terrain height data set obtained from NOAA. Terrain heights in kilometers (km) were converted to millibars (mb) using the following equation:
where H is the terrain height in km.
The entire globe is divided into 2.5 x 2.5 degree latitude and longitude cells with terrain pressure given for each cell. A total of 10,585 values are given. A two-dimensional interpolation procedure using the four closest grid points is used to find the value of terrain pressure at the start of each major frame. Surface pressure is supplied for discrete mode data only.
The Ancillary Data Set contains the thirteen SBUV/2 bandcenter wavelengths, their associated ozone absorption and Rayleigh scattering coefficients, total ozone and multiple scattering correction lookup tables, and the a priori profiling information. This is the data required to initialize the ozone algorithm.
The Multiple Scattering Coefficients data records contain 1700 values (10 solar zenith Angles, 23 standard ozone profiles, five wavelengths and two surface pressures) of Log Q, 1700 values of Log Q (single scattered), 1700 values of reflected fraction and 170 values (for 23 standard ozone profiles, five wavelengths and two surface pressures) of atmospheric-surface backscatter fraction). The Total Ozone Tables data records contain 1700 values of Log I0, 1700 values of reflected fraction, and 170 values of atmospheric-surface backscatter fraction. The A-Priori Profile Information data records will contain 180 values of a priori profile coefficients and 144 values for the a priori covariance matrix elements.
As the ancillary data is not time dependent, this data will be written one for each Daily 1b Data set.
The Instrument Calibration and Albedo Correction Data contains four sets of values:
Initially, only prelaunch radiance and irradiance calibrations will be on the 1b Data Set until the Instrument Support Subsystem is implemented. Three sets of prelaunch calibration values are required:
The radiance and irradiance calibrations each consist of 37 constants: one value for the CCR at 3786.2 Å and 12 values for each of the three monochromator gain ranges at the 12 discrete wavelengths. The ratios of the radiance and irradiance calibrations are used in the computation of I/F ratios in the ozone computation. The prelaunch flux ratios will be used to perform the diffuser calibration in the instrument support subsystem. There will be one ratio for each mercury line chosen which is to be specified.
The monochromator interrange ratios and albedo correction factors are derived from the previous N (to be specified) day's instrument outputs for the current day 1b and ozone processing. There are two interrange ratios for the monochromator, one between gain ranges 1 and 2 (IRR21) and one between gain ranges 2 and 3 (IRR32).
The albedo corrections account for solar flux and instrument changes and are used to adjust the I/F ratios in the ozone processing; there are 13 values for a day, one for the CCR wavelength (3786.2 Å) and twelve for the monochromator discrete wavelengths.
The 1b Data Set contains a comprehensive set of flags that provide instrument status and data quality information. Table 22.214.171.124.7-1 summarizes the types of flags, where in the processing system they are set and what ranges of data they cover. The flags are defined in the Data Dictionary (Section 9.7.5).
|Data Quality Flags||Where Set*||Data Range Covered|
|Minor Frame Quality Flags||Decommutation||Channel|
|Major Frame Quality Flags||Raw TIP/ Decommutation Immediate||Major Frame|
|Final Channel Quality Flags||1b||Channel|
|Channel Fill Flags||1b||Channel|
|Channel Error Flags||1b||Channel|
|Sample Status Flags||1b||1 discrete sample
10 sweep samples
|Summary Status Flags|
|Summary Grating Mode||1b||Major Frame**|
|Summary Grating Memory Mode||1b||Major Frame**|
|Scene Mode||1b||Major Frame**|
|Channel=10 minor frames=1 second|
|Major frame=320 minor frames=32 seconds|
|Discrete sample=2 second interval|
|10 Sweep samples=1 second interval|
|*Refer to Section 1.5 for a discussion of the step for the Operational Ozone Product System
**Based on major frames where ECAL/Retrace is off.
For the start time of each TIP Major Frame (every 32 seconds), using as input the ephemeris (i.e. spacecraft position and velocity vectors) data from GTDS, the following earth location parameters are derived.
A fill value may be inserted into an individual data item on the 1b Data Set to indicate that the original data in the input data stream was missing. The Daily Headers and Ancillary Data contain no fill values. The only record types which contain fill values in the Daily Data Records files of the 1b Data Set are the Discrete and Sweep Data Records. Fill values for data items or groups of data items are given in Table 126.96.36.199.9-1.
|Data Items or Group of Data Items||Fill Values||Comment|
(Hex Code 8001)
|Reason for fill given by Major Frame Quality Dwell Mode, Data Fill or Missing Attitude Flags|
|Earth Location Data||-32,767||Reason for fill is no Earth Location Data Found by Decommutation Program (Indicated by Major Frame Quality Flag For No Earth Location Data)|
|Digital B Telemetry & Data and Analog||All Bits set to 1||Reason for fill given in this frame's and possibly next frame's Major Frame Quality Flag: Dwell Mode, or Data Fill Flags|
|Digital A Instrument Data except Recommended Monochromator Range I. D.||Reason for fill given by Major Frame Quality Flags: Data Fill Flags|
|Meteorological and Geographical Support Data except for FOV Snow/Ice Flag, Cloud Amount/Cloud Albedo and Cloud Amount for Spots 1-9||-7777||Cloud top pressure set to -7777 when no clouds present in 8 second SBUV/2 FOV (i.e. cloud amount = 0)|
|Cloud Amount/Cloud Albedo||-1028|
|Cloud Amount for Spots 1-9||-8|
|FOV Snow/Ice Flag Digital A||-1|
|Digital A Analog Housekeeping Data||All bits set to 1||Reason for fill given by Major Frame Quality Flags: Dwell Mode or Data Fill Flags|
|Total Ozone and Profile||-77.0||Reason given by corresponding Ozone Data Error Flag|
|Note: this table includes some data items not found in the 1b Data Set.|
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