ILRS Normal Point Format and Data Integrity Algorithm

The following ILRS Normal Point (NP) quality control procedures for NP format and data integrity were implemented Thursday, 24 February 2000 at the NASA SLR Operations Center. These procedures were presented and approved at the Data Formats and Procedures WG meeting in Florence, Italy (September 1999).

Stations are encouraged to build these checks into their data processing system to enable the earliest possible detection of a problem.

NP FORMAT and DATA INTEGRITY ALGORITHMS (FEB 2000)

An ILRS NP pass/pass segment must meet the following two ILRS standards for format and data integrity. A pass which does not meet these standards will be placed in a bad file. The station will be notified via email of the non-conformance issue and will be responsible for fixing the error and resupplying the corrected NP data.

1. ILRS NP FORMAT COMPLIANCE

An ILRS NP pass is considered in the proper ILRS NP Format if ALL of the following four conditions are meet (Note: a pass can be part of a pass (i.e., pass segment) or an entire pass, but not two passes within a single pass):

a. The first line of the NP pass consists of five '9's starting in column 1.

b. The second line of the NP pass consists of a valid header record. A valid header record must have a record length or 54 or 55 bytes and the first 54 bytes must be NUMERIC or a '-'. (i.e., non-blank, no special characters except for a '-', and no letters from the alphabet)

c. The third and each succeeding line of the NP pass are valid NP data record(s). A valid NP data record must have a record length of 54 bytes and all 54 bytes must be NUMERIC. Note: There must be a least one NP record to be considered a valid pass.

d. The NPs are from the same satellite revolution (i.e., can not have 2 or more passes with a single header record)

For example, below is considered a valid pass with "m" NP records: 

99999
[Valid Header Record]
[Valid Normal Point Data Record 1]
[Valid Normal Point Data Record 2]
...
...
...
[Valid Normal Point Data Record m]

2. ILRS NP DATA INTEGRITY COMPLIANCE

Data integrity is totally independent of format integrity. Data integrity placed conditions on the values of certain fields within the ILRS NP header and ILRS NP data records.

2.1 Header Record

The following fields within the header record will be validated.

a. Columns 1-7: The ILRS 7-digit satellite identifier must be valid. (note: This number is a derived from the COSPAR identification).

b. Columns 10-12: The day of year must be between 1 and 365 for non leap yea rs and must be between 1 and 366 for leap years.

c. Columns 13-20: The Site Occupancy Designator (SOD) must be a current valid SOD (note: the SOD is assigned by the CDDIS).

2.2 Data Record

The following fields within the data record will be validated.

a. Bytes 1-12: Time of laser firing must be between 0 and 863999999999 tenths of microseconds (i.e. > 0 seconds and < 86400 seconds), inclusive.

b. Bytes 32-36: Surface pressure must be between 6000 and 11000 tenths of millibars (i.e., between 600 and 1100 millibars), inclusive.

c. Bytes 37-40: Surface temperature must be between 2000 and 3400 tenths of degrees Kelvin, inclusive.

d. Bytes 41-43: Humidity must be between 0 and 100 percent, inclusive.

Additional checks will also be performed on the NPs to ensure they adhere to the ILRS Satellite Bin Size Standard and adhere to the Herstmonceux Bin Formation Algorithm. Any passes containing NPs that do not pass these criterion will still be delivered to the ILRS Data Centers, but the station will be notified electronically of any NP bin compliance issues.

3. ILRS NP BIN COMPLIANCE

a. Header Record Byte 43: The Normal Point Window Indicator must be the ILRS agreed bin size for that particular satellite.

b. Bin formation is based from 0 Hours UTC (i.e., not from the epoch of the first observation). The algorithm to test for this is:

two consecutive NP will not have the same integer quotient when their corresponding NP epochs (in seconds) divided by the appropriate satellite bin size (in seconds).

Example: if NP epoch(i)/bin size = NP epoch(i+1)/bin size then there is a bin formation violation