spacer link to MAST page spacer logo image spacer
link to STScI page

HST File Naming Convention


HST data use the 'ipppssoot' file naming convention. Each letter is mapped as follows:

i : Instrument identifier; will be one of:

F = Astrometry (FGS),
I = Wide Field Camera 3 (WFP3),
J = Advanced Camera for Surveys (ACS),
L = Cosmic Origins Spectrograph (COS),
N = Near Infrared Camera and Multi-Object Spectrograph (NICMOS),
O = Space Telescope Imaging Spectrograph (STIS),
S = Engineering subset data,
U = Wide Field/Planetary Camera-2 (WFPC2),
V = High Speed Photometer (HSP),
W = Wide Field/Planetary Camera (WFPC),
X = Faint Object Camera (FOC),
Y = Faint Object Spectrograph (FOS),
Z = Goddard High Resolution Spectrograph (HRS)

ppp : Program ID; can be any combination of 3 letters or numbers. There is a unique association between program ID and proposal ID (generally equivalent to the 5-digit HST phase-2 ID),

ss : Observation set ID (generally, but not always, equivalent to the HST phase-2 visit number); any combination of 2 letters or numbers.

oo : Observation number, a.k.a. 'obsnum' (generally unique for each exposure); any combination of 2 letters or numbers.

t : Source of transmission character. At launch, 't' indicated the source of the data: real time (R), tape recorder (T) or merged real time, and taped data (M). Over the years, as data ingestion has changed, the use of 't' has changed. It is simply an indicator of whether or not a better version of the data have been received. The most common sequence for the modern instruments is Q, S, where S is the retransmitted better version. The full set of possible values for 't' are:

B = B-associations generated by CADC and ST-ECF for WFPC2,
M = Merged real time and tape recorded***,
N = Retransmitted merged real time and tape recorded*,
O = Retransmitted real time (letter 'O’)*,
P = Retransmitted tape recorded*,
Q = Solid-state recorder (post Servicing Mission-2)**,
R = Real time (not recorded)***,
S = Retransmitted solid-state recorder (post Servicing Mission-2)**,
T = Tape recorded***,

* Note: Retransmissions between the Data Capture Facility and STScI of better versions.
** Note: Post Servicing Mission-2, all data were Q, except when a better version was sent from PACOR, and then it was S.
*** Note: For WFPC2, it started as T, changed to R, then to M a few years later, where it remained until WFPC2 was removed from HST.

'oot' Alternative : Association/product; introduced with NICMOS and STIS. These collections of exposures are created in the pre-archive pipeline and so do not need a transmission source ('t'). The three characters comprising the obsnum ('oo') and the transmission source ('t') are used to distinguish an association from an exposure. The syntax, usually represented as '0nm', allowed for products and subproducts, with '010' being the first product in a given obset (visit) and '011' being the first subproduct for that first product. An example of a subproduct is a NICMOS background exposure. Most products do not have subproducts. With the installation of ACS, the product/subproduct relation was broken as ACS designated the "prime" product, '0n0', as the dither product. Any non-dither ACS or WFC3 product is designated '0n1'.****

Note****: The '0nm' syntax is misleading as products, such as O45P01Z10, OBPW013Z0, and J8ZS0502B exist.

HST Data Suffix

HST data use a number of suffix rules after the 'ipppssoot' name.


SuffixDescriptionUsed with the following Instrument(s)
_raw Raw data WFC3, ACS, NICMOS, STIS
_tag Raw timetag data STIS
_lrc Local rate check image (BOP) STIS
_wav Wavecal STIS
_wsp Wavecal support file STIS
_asn Association file WFC3, ACS, COS, NICMOS, STIS
_spt Telescope, telemetry, engineering WFC3, ACS, COS, NICMOS, STIS
_trl Trailer, processing log WFC3, ACS, COS, NICMOS, STIS
_rawacq Raw data COS
.d0h/.d0d Science data image FOS, GHRS, WFPC1, WFPC2, FOC
.q0h/.q0d Science data quality FOS, GHRS, WFPC1, WFPC2, FOC


SuffixDescriptionUsed with the following Instrument(s)
_flt Calibrated, flat-fielded exposure WFC3, ACS, STIS
_crj Calibrated, CR-rejected, combined WFC3, ACS, STIS/CCD
_drz Calibrated, geometrically-corrected, dither-combined WFC3 ACS
_fltsum Calibrated, flat-field for images COS
_x1dsum Calibrated, combined 1D extracted for spectra COS
_x1d Calibrated 1D spectra from exposures STIS
_x2d Calibrated 2Dspectra/images from exposures STIS
_sx1 Calibrated 1D spectra from combined exposures STIS
_sx2 Calibrated 2D spectra/images from combined exposures STIS
_cal Calibrated exposure NICMOS
_mos Calibrated, combined image NICMOS
_sfl Summed, flat-fields image STIS/MAMA
.c0h/.c0d Calibrated wavelengths FOS, GHRS
.c1h/.c1d Calibrated fluxes FOS, GHRS
.cqh/cqd Calibrated science data quality FOS, GHRS
.c0h/.c0d Calibrated science data WFPC1, WFPC2, FOC
.q0h/.q0d Calibrated science data quality WFPC1, WFPC2, FOC


  1. Dataset name, F05Q7407M, where 'ipppssoot' is mapped as follows:

    i=F (FGS)
    t=M (Merged)
  2. Here is an example of a NICMOS product, with two background subproducts. The subproducts are considered members of the product.

    data_set_name: type:
    N4RK05010 PROD-TARG
    N4RK05011 PROD-BCK1
    N4RK05012 PROD-BCK2
  3. ACS adopted the convention that the mn0 product would always be a dither product. Since not all ACS exposures result in a dither product, the 0n1 product is frequently the only product/association produced. Care should be taken to ensure a product is not confused with a subproduct. WFC3 continues this convention. Here is an example of an ACS repeat obs product.

    data_set_name: type:
    J8AN01011 PROD-RPT

Additional examples and information can be found in older, html-versions of the HST Handbook and here. A full list of up-to-date HST Handbooks can be found here.