ILRS Normal Point (NP) Data

Normal Point (NP) data is the primary ILRS station data product. Normal points gradually replaced on-site sampled data and later fullrate data as the primary station data product. Normal points are sometimes referred to as quick-look data, because the normal points are generated very shortly after the satellite pass and transimitted rapidly (within a few hours) to the data centers.

The ILRS continues to strive for improvement in data reliability. At its meeting in Nice 2002, the ILRS Governing Board adopted a minimum data requirement for SLR normal points. This requirement, adopted at the recommendation of the Networks and Engineering Working Group is as follows:

Daytime normal points - minimum 6 data points
Night time normal points - minimum 3 data points
Fewer data points would be acceptable on lower satellites (5-second normal points) from those ranging systems with lower pulse repetition rates where these minimum requirements are not practical.

However, at the IGS Technical Workshop, held in Koetzting in October 2003, it was recommended that stations may exercise their own discretion in setting minimum data criteria per normal point or disregard them all together. The ILRS Governing Board recommends the Nice 2002 criteria (6 data points per NP in daylight and 3 data points per NP at night) for single photoelectrons systems with high data yield. Stations with KHz return rates may select more stringent criteria. Stations must include their minimum NP data criteria as a note in their Site Logs.

A second revision to the normal point format was approved in August 2004 and announced in SLRMail 1248 to accomodate data from kHz ranging systems since the returns from these systems exceed the maximum value available in the format (9999 points per normal point).

The CDDIS has interactive queries of NP data volume (by year and station, by year and satellite).

Related Links:

Table of satellite information including NP bin size
Station Data Anomalies (i.e., range biases, time biases, frequency error, barometer errors, etc.) and CDDIS Bulletin Data Bits and Bytes

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