The Core Data File

Filename conventions

The core file is named as core_faam_<date>_<version>_<revision>_<fltnum>[_<freq>].nc, where:

• date indicates the date on which the flight took place, formatted as YYYYmmdd, where YYYY is the four-digit year, mm is the two-digit month, and dd is the two-digit day.

• version indicates the version of the core file, formatted as vnnn, where nnn is a three-digit integer. The most recent version is 5 (v005), which this document applies to. It is important to note that older versions do not strictly follow the conventions outlined in this document.

• revision indicates the revision number of the data, formatted as rn, where n is an integer. Larger values of n indicate a more recent release. Where more than one data revision is available, the file with the largest revision number should be used.

• fltnum indicates the flight number of the flight, formatted as xnnn where x is a lowercase letter, and nnn a three digit integer.

• freq indicates the frequency of the dataset, formatted as nhz, where n is an integer. If not present, the file is at ‘full’ frequency, with the frequency differing between variables. Typically ‘full’ and 1hz files are provided.

Dimensions

All variables in the core dataset are timeseries with the same start and end times, and with frequencies of 1 Hz or greater. There is only one time dimension, Time, with a length equal to the duration of the dataset in seconds. Variables which are recorded at 1 Hz will have Time as their only dimension. Variables which are recorded at higher than 1 Hz will be stored as a two-dimensional array, with Time as the first dimension and spsNN as the second. Here, the NN repesents the frequency in Hz. For example, a 4 Hz variable would have dimensions Time and sps04, and would be stored as an \(n\times4\), where n is the length of the dataset in seconds.

The dimensions which may be included in the full temporal resolution core data file are:

• Time - An unlimited dimension whose length corresponds to the length of the dataset, in seconds.

• sps02 - 2 samples per second. A dimension of length 2.

• sps04 - 4 samples per second. A dimension of length 4.

• sps10 - 10 samples per second. A dimension of length 10.

• sps20 - 20 samples per second. A dimension of length 20.

• sps32 - 32 samples per second. A dimension of length 32.

• sps64 - 64 samples per second. A dimension of length 64.

Global Attributes

Required Global Attributes

• Conventions - The conventions followed by this data

• acknowledgement - The acknowledgement for use of this data. Should read: Airborne data was obtained using the BAe-146-301 Atmospheric Research Aircraft [ARA] flown by Airtask Ltd and managed by FAAM Airborne Laboratory, jointly operated by UKRI and the University of Leeds for FAAM data.

• creator_address - The address of the FAAM offices. Should read: Building 146, Cranfield University, College Road, Cranfield, Bedford. MK43 0AL. UK. for FAAM data.

• creator_email - The email address of the data creator, or a generic FAAM email.

• creator_institution - The institute responsible for the creation of the data. Should read: FAAM Airborne Laboratory for FAAM data

• creator_name - The name of the person or institute responsible for this data

• creator_type - The type of creator. Should be one of person, institution, position

• date - Date of the flight

• date_created - ISO:8601 date/time file created, ideally yyyy-mm-ddTHH:MM:SSZ. Equivalent to revision_date.

• flight_date - Date of the flight

• flight_number - The flight number

• geospatial_bounds - A well-known text representation of the flight envelope

• geospatial_bounds_crs - Coordinate reference system for geospatial attributes.

• geospatial_lat_max - Maximum latitude of the flight.

• geospatial_lat_min - Minimum latitude of the flight.

• geospatial_lat_units - The units for geospatial_lat_* attributes

• geospatial_lon_max - Maximum longitude of the flight

• geospatial_lon_min - Minimum longitude of the flight

• geospatial_lon_units - The units for geospatial_lon_* attributes

• geospatial_vertical_max - The maximum altitude of the flight

• geospatial_vertical_min - The minimum altitude of the flight

• geospatial_vertical_units - Vertical units associated with geospatial_vertical_* attributes

• geospatial_vertical_positive - Positive direction of geospatial_vertical_* attributes

• id - filename without extension, needs to be globally unique w/ naming_authority

• institution - The institute responsible for the creation of this data. Should read: FAAM Airborne Laboratory for FAAM data.

• keywords - A comma separated list of keywords from the GCMD

• keywords_vocabulary - Controlled vocabulary for keywords. Should read Global Change Master Directory (GCMD)

• license - The license for this data. Should read: UK Government Open Licence agreement - http://www.nationalarchives.gov.uk/doc/open-government-licence

• metadata_link - A link to a release of a controlled vocabulary of metadata attributes

• naming_authority - The authority responsible for naming this data. Should read uk.ac.faam

• platform - Platform name of the FAAM aircraft. Should read: FAAM BAe-146-301 Atmospheric Research Aircraft

• platform_type - Platform type: aircraft

• project - The project a flight was for. Expected to be of the form <project_acronym> - <project_name>

• publisher_email - The email address of the data publisher

• publisher_institution - The institution responsible for publishing data. Should read: CEDA

• publisher_type - Type of entity responsible for publishing data. Should be institution

• publisher_url - The URL of the data publisher. Should be https://www.ceda.ac.uk

• references - A list of references relevant to the file

• revision_date - The date this revision created. Analogous to date_created

• revision_number - The revision number of the dataset. Starts at 0, increments by 1 for each revision

• source - A description of the source of the data. An instrument where this makes sense, otherwise a description of how data obtained

• standard_name_vocabulary - A vocabulary of standard names. Expected to be a CF standard name table, e.g. CF Standard Name Table v78

• summary - A brief summary of the data

• time_coverage_duration - The duration of the data, in ISO8601 duration format

• time_coverage_start - The start time of the data in the file, in ISO8601 format

• time_coverage_end - The end time of the data in the file, in ISO8601 format

• title - A brief title for the dataset

• uuid - V3 UUID: MD5 hash of id+date_created

Optional Global Attribtues

• calibration_date - Calibration date, where this applies to all file contents

• calibration_information - Calibration information, where this applies all file contents

• calibration_url - Permanent URI or DOI linking to calibration info, where this applies to all file contents

• comment - Comment about data

• constants_file - Name of external file providing input to processing software

• creator_url - Institutional URL or researcher ORCID URL

• deployment_mode - Mode of deployment. Should always be “air”

• external_variables - Blank separated list of variables used from an external file

• history - Logs modifications to file since production

• instrument - Where all data id from a single instrument. Currently freeform, controlled instrument vocab to follow

• instrument_description - Where all data are from a single instrument. Textual description.

• instrument_location - Where all data are from a single instrument. Location of instrument on aircraft

• instrument_manufacturer - Where all data are from a single instrument. Instrument manufacturer

• instrument_model - Where all data are from a single instrument. Instrument model

• instrument_serial_number - Where all data are from a single instrument. Instrument serial number

• instrument_software - Where all data are from a single instrument. Name of software deployed on instrument

• instrument_software_version - Where all data are from a single instrument. Version of software deployed on instrument

• notes - Notes on this data file. For more detailed info than comment

• processing_software_commit - Commit hash for processing software in vcs

• processing_software_doi - DOI of the processing doftware release, if available

• processing_software_url - URL pointing to processing software source code, if available

• processing_software_version - Version of processing software

• project_acronym - Project acronym

• project_name - Full project name

• project_principal_investigator - Name(s) of project PIs. Comma separated if more than one

• project_principal_investigator_email - Email address(es) of project PIs. Comma separated if more than one

• project_principal_investigator_url - ORCID URL(s) of project PIs. Comma separated if more than one

• revision_comment - Brief description of changes between revisions

• source_files - List of source files used in the processing of this data product

• time_coverage_resolution - Resolution of data, where this is uniform across the file

• processing_level - Processing level of data, where it is uniform for all data in the file

Variable Attributes

Required Variable Attributes

• _FillValue - The prefill/missing data value

• coverage_content_type - ISO 19115-1 code. One of image, thematicClassification, physicalMeasurement, auxiliaryInformation, qualityInformation, referenceInformation, modelResult, coordinate

• frequency - The frequency of the data. Where this is >1, will typically correspond to an spsNN dimension

• long_name - A longer, descriptive name for the variable

• units - Valid UDUNITS unit. Where a standard_name is given, must be equivalent to canonical units

Optional Variable Attributes

• axis - Axis for coordinate variables. Should be one of X, Y, Z, T

• actual_range - A length 2 array, of the same datatype as the variable, giving the maximum and minimum valid values

• add_offset - Offset for packing. Default is 0

• ancillary_variables - Optional in no ancillary variables, otherwise required. Ancillary variables e.g. flags, uncertainties

• calendar - Required for the time coordinate variable. Should be one of standard, gregorian

• calibration_date - Calibration date, where this applies to variable

• calibration_information - Calibration information, where this applies variable

• calibration_url - Permanent URI or DOI linking to calibration info, where this applies to variable

• comment - Comment about data

• coordinates - Blank separated list of coordinate variables

• flag_masks - Allowed flag mask values. Required for bitmask style flags

• flag_meanings - Blank separated list of flag meanings. Required for flag variables

• flag_values - Allowed flag values. Required for classic flags

• instrument_description - Textual description of instrument.

• instrument_location - Where variable is derived from a single instrument. Location of instrument on aircraft

• instrument_manufacturer - Where variable is derived from a single instrument. Instrument manufacturer

• instrument_model - Where variable is derived from a single instrument. Instrument model number

• instrument_serial_number - Where variable is derived from a single instrument. Instrument serial number

• instrument_software - Where variable is derived from a single instrument. Name of software deploed on instrument

• instrument_software_version - Where all data in the group are from a single instrument. Version of software deployed on instrument

• sensor_manufacturer - Similar to instrument_manufacturer, but where the item is more accurately described as a sensor

• sensor_model - Similar to instrument_model, but where the item is more accurately described as a sensor

• sensor_serial_number - Where variable is derived from a single sensor, similar to instrument_serial_number. Sensor serial number.

• sensor_type - The type of sensor fitted, where different sensor types may be used to produce the same measurement. A canonical example of this is the type of temperature sensor in the Rosemount housings.

• positive - Applies to vertical coordinate. Should be “up” if included

• scale_factor - Scale for packing. Default is 1

• standard_name - See CF standard names list. Should be used whenever possible

• valid_max - Recommended where feasible. Where both valid_min and valid_max make sense, valid_range is preferred.

• valid_min - Recommended where feasible. Where both valid_min and valid_max make sense, valid_range is preferred.

• valid_range - A length 2 array of the same datatype as the variable, giving minimum and maximum valid values

• processing_level - Processing level of variable data

Variables

Below is a list of all output variables which can be created during postprocessing, split into variables which will always be written to file if available, and those which are generally only used internally, but which can be written to file if requested. Note that some variables may be duplicated here. This indicates that the same output variable may be produced from two or more processing modules, depending on the fit of the aircraft. These will be mutually exclusive, so that variables will be unique in a dataset.

Written if Available

Default Variables

Name	Long Name	Standard Name	Processing Module
ACLD_GIN	Acceleration along the aircraft vertical axis from POS AV 410 GPS-aided Inertial Navigation unit (positive down)		Gin
ACLF_GIN	Acceleration along the aircraft longitudinal axis from POS AV 410 GPS-aided Inertial Navigation unit (positive forward)		Gin
ACLS_GIN	Acceleration along the aircraft transverse axis from POS AV 410 GPS-aided Inertial Navigation unit (positive starboard)		Gin
ALT_GIN	Altitude from POS AV 410 GPS-aided Inertial Navigation unit	altitude	Gin
AOA	Angle of attack from the turbulence probe (positive, flow upwards wrt a/c axes)		TurbulenceProbe
AOSS	Angle of sideslip from the turbulence probe (positive, flow from left)		TurbulenceProbe
BSC_BLUU	Uncorrected blue back scattering coefficient from TSI 3563 Nephelometer		Nephelometer
BSC_GRNU	Uncorrected green back scattering coefficient from TSI 3563 Nephelometer		Nephelometer
BSC_REDU	Uncorrected red back scattering coefficient from TSI 3563 Nephelometer		Nephelometer
BTHEIM_U	Uncorrected brightness temperature from the Heimann radiometer		Heimann
CAB_PRES	Cabin Pressure		CabinPressure
CAB_TEMP	Cabin temperature at the core consoles		CabinTemp
CO_AERO	Mole fraction of Carbon Monoxide in air from the AERO AL5002 instrument	mole_fraction_of_carbon_monoxide_in_air	AL52CO
CPC_CNTS	Condensation Particle Counts measured by the TSI 3786		CPC
EXX_JCI	Raw data from the Fwd Core Console JCI static monitor, static signal		ElectricFieldJci140
EXX_ZEUS	Electric field measured by the Zeus instrument		ElectricFieldZeus
GSPD_GIN	Groundspeed from POS AV 410 GPS-aided Inertial Navigation unit	platform_speed_wrt_ground	Gin
HDGR_GIN	Rate-of-change of heading from POS AV 410 GPS-aided Inertial Navigation unit	platform_yaw_rate	Gin
HDG_GIN	Heading from POS AV 410 GPS-aided Inertial Navigation unit	platform_yaw_angle	Gin
HGT_RADR	Radar height from the aircraft radar altimeter	height	RadAlt
IAS_RVSM	Indicated air speed from the aircraft RVSM (air data) system		AirSpeed
IR_DN_C	Corrected downward longwave irradiance		KippZonenPyrgeometer
IR_UP_C	Corrected upward longwave irradiance		KippZonenPyrgeometer
LAT_GIN	Latitude from POS AV 410 GPS-aided Inertial Navigation unit	latitude	Gin
LON_GIN	Longitude from POS AV 410 GPS-aided Inertial Navigation unit	longitude	Gin
NEPH_PR	Internal sample pressure of the Nephelometer		Nephelometer
NEPH_RH	Relative humidity from TSI 3563 Nephelometer		Nephelometer
NEPH_T	Internal sample temperature of the Nephelometer		Nephelometer
NV_LWC1_C	Corrected liquid water content from the Nevzorov probe (1st collector)	mass_concentration_of_liquid_water_in_air	Nevzorov
NV_LWC1_U	Uncorrected liquid water content from the Nevzorov probe (1st collector)		Nevzorov
NV_LWC2_C	Corrected liquid water content from the Nevzorov probe (2nd collector)	mass_concentration_of_liquid_water_in_air	Nevzorov
NV_LWC2_U	Uncorrected liquid water content from the Nevzorov probe (2nd collector)		Nevzorov
NV_LWC_C	Corrected liquid water content from the Nevzorov probe	mass_concentration_of_liquid_water_in_air	Nevzorov
NV_LWC_U	Uncorrected liquid water content from the Nevzorov probe		Nevzorov
NV_TWC_C	Corrected total condensed water content from the Nevzorov probe		Nevzorov
NV_TWC_U	Uncorrected total condensed water content from the Nevzorov probe		Nevzorov
O3_2BTECH	Mole fraction of Ozone in air from the 2BTech photometer	mole_fraction_of_ozone_in_air	TwoBOzone
O3_TECO	Mole fraction of Ozone in air from the TECO 49 instrument	mole_fraction_of_ozone_in_air	TeiOzone
P0_S10	Calibrated differential pressure between centre (P0) port and S10 static		TPress
P10_STAT	Static pressure from S10 fuselage ports	air_pressure	S10Pressure
P9_STAT	Static pressure from S9 fuselage ports	air_pressure	S9Pressure
PALT_RVS	Pressure altitude from the aircraft RVSM (air data) system	barometric_altitude	Rvsm
PA_TURB	Calibrated differential pressure between turbulence probe vertical ports		TPress
PB_TURB	Calibrated differential pressure between turbulence probe horizontal ports		TPress
PITR_GIN	Rate-of-change of pitch angle from POS AV 410 GPS-aided Inertial Navigation unit	platform_pitch_rate	Gin
PSAP_FLO	PSAP Flow		PSAP
PSAP_LIN	Uncorrected absorbtion coefficient at 565nm, linear, from PSAP		PSAP
PSAP_LOG	Uncorrected absorption coefficient at 565nm, log, from PSAP		PSAP
PSAP_TRA	PSAP Transmittance		PSAP
PSP_TURB	Pitot-static pressure from centre-port measurements corrrected for AoA and AoSS		TurbulenceProbe
PS_RVSM	Static pressure from the aircraft RVSM (air data) system	air_pressure	Rvsm
PTCH_GIN	Pitch angle from POS AV 410 GPS-aided Inertial Navigation unit	platform_pitch_angle	Gin
Q_RVSM	Pitot static pressure inverted from RVSM (air data) system indicated airspeed		Rvsm
RED_DN_C	Corrected downward short wave irradiance, red dome		BBRFlux
RED_UP_C	Corrected upward short wave irradiance, red dome		BBRFlux
RH_ICE	Relative humidity wrt ice water, derived from corrected WVSS-II VMR and Rosemount temperatures	relative_humidity	WVSS2RH
RH_ICE_CU	Combined uncertainty estimate for RH_ICE		WVSS2RH
RH_LIQ	Relative humidity wrt liquid water, derived from corrected WVSS-II VMR and Rosemount temperatures	relative_humidity	WVSS2RH
RH_LIQ_CU	Combined uncertainty estimate for RH_LIQ		WVSS2RH
ROLL_GIN	Roll angle from POS AV 410 GPS-aided Inertial Navigation unit	platform_roll_angle	Gin
ROLR_GIN	Rate-of-change of roll angle from POS AV 410 GPS-aided Inertial Navigation unit	platform_roll_rate	Gin
SEA_LWC_021	Liquid water content from the SEA WCM-2000 probe, element 021	mass_concentration_of_liquid_water_in_air	SeaProbe
SEA_LWC_083	Liquid water content from the SEA WCM-2000 probe, element 083	mass_concentration_of_liquid_water_in_air	SeaProbe
SEA_TWC_021	Total water content from the SEA WCM-2000 probe, element 021		SeaProbe
SEA_TWC_083	Total water content from the SEA WCM-2000 probe, element 083		SeaProbe
SO2_TECO	Mole fraction of Sulphur Dioxide in air from TECO 43 instrument	mole_fraction_of_sulfur_dioxide_in_air	TecoSO2V2
SO2_TECO	Mole fraction of Sulphur Dioxide in air from TECO 43 instrument	mole_fraction_of_sulfur_dioxide_in_air	TecoSO2
SOL_AZIM	Solar azimuth derived from aircraft position and time	solar_azimuth_angle	SolarAngles
SOL_ZEN	Solar zenith derived from aircraft position and time	solar_zenith_angle	SolarAngles
STATUS_GIN	Solution status from POS AV 410 GPS-aided Inertial Navigation unit		Gin
SW_DN_C	Corrected downward short wave irradiance, clear dome	downwelling_shortwave_flux_in_air	BBRFlux
SW_UP_C	Corrected upward short wave irradiance, clear dome	upwelling_shortwave_flux_in_air	BBRFlux
TAS	True airspeed (dry-air) from turbulence probe	platform_speed_wrt_air	TurbulenceProbe
TAS_RVSM	True air speed from the aircraft RVSM (air data) system and deiced temperature	platform_speed_wrt_air	AirSpeed
TAT_DI_R	True air temperature from the Rosemount deiced temperature sensor	air_temperature	PRTTemperatures
TAT_DI_R	True air temperature from the Rosemount deiced temperature sensor	air_temperature	ThermistorV1Temperatures
TAT_DI_R_CU	Combined uncertainty estimate for TAT_DI_R		PRTTemperatureUncertainties
TAT_ND_R	True air temperature from the Rosemount non-deiced temperature sensor	air_temperature	PRTTemperatures
TAT_ND_R	True air temperature from the Rosemount non-deiced temperature sensor	air_temperature	ThermistorV1Temperatures
TAT_ND_R_CU	Combined uncertainty estimate for TAT_ND_R		PRTTemperatureUncertainties
TDEWCR2C	Corrected dew point temperature measured by the Buck CR2 Hygrometer	dew_point_temperature	BuckCR2
TDEW_CR2	Mirror Temperature measured by the Buck CR2 Hygrometer	dew_point_temperature	BuckCR2
TDEW_C_U	Combined uncertainty estimate for Buck CR2 Mirror Temperature		BuckCR2
TDEW_GE	Dew Point from the General Eastern instrument	dew_point_temperature	GeneralEastern
TRCK_GIN	Aircraft track angle from POS AV 410 GPS-aided Inertial Navigation unit	platform_course	Gin
TSC_BLUU	Uncorrected blue total scattering coefficient from TSI 3563 Nephelometer		Nephelometer
TSC_GRNU	Uncorrected green total scattering coefficient from TSI 3563 Nephelometer		Nephelometer
TSC_REDU	Uncorrected red total scattering coefficient from TSI 3563 Nephelometer		Nephelometer
U_C	Eastward wind component from turbulence probe and GIN	eastward_wind	TurbulenceProbe
U_NOTURB	Eastward wind component derived from aircraft instruments and GIN	eastward_wind	GINWinds
VELD_GIN	Aircraft velocity down from POS AV 410 GPS-aided Inertial Navigation unit		Gin
VELE_GIN	Aircraft velocity east from POS AV 410 GPS-aided Inertial Navigation unit		Gin
VELN_GIN	Aircraft velocity north from POS AV 410 GPS-aided Inertial Navigation unit		Gin
VMR_CR2	Water vapour volume mixing ratio measured by the Buck CR2		BuckCR2
VMR_C_U	Combined uncertainty estimate for water vapour volume mixing ratio measured by the Buck CR2		BuckCR2
V_C	Northward wind component from turbulence probe and GIN	northward_wind	TurbulenceProbe
V_NOTURB	Northward wind component derived from aircraft instruments and GIN	northward_wind	GINWinds
WAND_GIN	Wander angle from POS AV 410 GPS-aided Inertial Navigation unit		Gin
WOW_IND	Weight on wheels indicator		WeightOnWheels
WVSS2F_PRESS_U	Pressure inside {ins} sample cell {interp}		WVSS2A
WVSS2F_VMR_C	Calibrated volume mixing ratio from WVSS2F		WVSS2Calibrated
WVSS2F_VMR_C_CU	Uncertainty estimate for calibrated volume mixing ratio from WVSS2F		WVSS2Calibrated
WVSS2F_VMR_U	Water Vapour Measurement from {ins} {interp}		WVSS2A
WVSS2R_PRESS_U	Pressure inside {ins} sample cell {interp}		WVSS2B
WVSS2R_VMR_U	Water Vapour Measurement from {ins} {interp}		WVSS2B
W_C	Vertical wind component from turbulence probe and GIN	upward_air_velocity	TurbulenceProbe

Used internally

Default Variables

Name	Long Name	Standard Name	Processing Module
ETA_DI	Variable recovery factor for deiced Rosemount housing		RecoveryFactor
ETA_DI_CU	Uncertainty in recovery factor for non-deiced Rosemount housing		RecoveryFactor
ETA_ND	Variable recovery factor for non-deiced Rosemount housing		RecoveryFactor
ETA_ND_CU	Uncertainty in recovery factor for deiced Rosemount housing		RecoveryFactor
IAT_DI_R	Indicated air temperature from the Rosemount deiced temperature sensor		PRTTemperatures
IAT_DI_R	Indicated air temperature from the Rosemount deiced temperature sensor		ThermistorV1Temperatures
IAT_DI_R_CU	Combined uncertainty estimate for IAT_DI_R		PRTTemperatureUncertainties
IAT_ND_R	Indicated air temperature from the Rosemount non-deiced temperature sensor		PRTTemperatures
IAT_ND_R	Indicated air temperature from the Rosemount non-deiced temperature sensor		ThermistorV1Temperatures
IAT_ND_R_CU	Combined uncertainty estimate for IAT_ND_R		PRTTemperatureUncertainties
LIRS	LWR I/R SIGNAL		BBRSols
LIRT	LWR I/R TEMP		BBRSols
LIRZ	LWR I/R ZERO		BBRSols
LP1S	LWR VIS CLR SIG		BBRSols
LP1T	LWR VIS CLR TEMP		BBRSols
LP1Z	LWR VIS CLR ZERO		BBRSols
LP2S	LWR VIS RED SIG		BBRSols
LP2T	LWR VIS RED TEMP		BBRSols
LP2Z	LWR VIS RED ZERO		BBRSols
MACH	Moist air Mach derived from WVSS-II(F) and RVSM		WetMach
MACH	Dry air Mach derived from and RVSM		DryMach
MACH_CU	Uncertainty estimate for moist-air Mach		WetMach
MACH_CU	Uncertainty estimate for MACH		DryMach
NV_CLEAR_AIR_MASK	Clear air mask based on Nevzorov Total Water power variance		Nevzorov
NV_LWC1_COL_P	LWC1 collector power		Nevzorov
NV_LWC2_COL_P	LWC2 collector power		Nevzorov
NV_LWC_COL_P	LWC collector power		Nevzorov
NV_LWC_REF_P	LWC reference power		Nevzorov
NV_REF_P	Reference power		Nevzorov
NV_TWC_COL_P	TWC collector power		Nevzorov
NV_TWC_REF_P	TWC reference power		Nevzorov
P9_STAT_U	Static pressure from S9 fuselage ports, uncorrected	air_pressure	S9Pressure
SH_GAMMA	Ratio of specific heats at constant pressure and constant pressure		WetMach
SH_GAMMA	Ratio of specific heats at constant pressure and constant pressure		DryMach
SH_GAMMA_CU	Uncertainty estimate for SH_GAMMA		WetMach
SH_GAMMA_CU	Uncertainty estimate for SH_GAMMA		DryMach
SO2_TECO_ZERO	TECO 43 SO2 interpolated zero		TecoSO2V2
SREG	Signal Register		SignalRegister
UIRS	UPP I/R SIGNAL		BBRSols
UIRT	UPP I/R TEMP		BBRSols
UIRZ	UPP I/R ZERO		BBRSols
UP1S	UPP VIS CLR SIG		BBRSols
UP1T	UPP VIS CLR TEMP		BBRSols
UP1Z	UPP VIS CLR ZERO		BBRSols
UP2S	UPP VIS RED SIG		BBRSols
UP2T	UPP VIS RED TEMP		BBRSols
UP2Z	UPP VIS RED ZERO		BBRSols

Flags

Every variable has an associated flag variable named <variable_name>_<postfix>, and referenced in the variable’s ancillary_variables attribute, which provides some quality or situational information about the data in the variable. There are two different flagging strategies used in the core data file; the first is a value-based quality flag, referred to as a value-based or classic flag, and the second is a packed boolean representation. Flagging is largely automatic, other than the flagged_in_qc flag meaning, which indicates that in the opinion of the person performing the quality control, that data should be treated with caution. It is up to the user to decide whether or not to use data which has been flagged. If in doubt, users should contact FAAM for advice.

Value-based Flags

Value-based flags represent the quality of the corresponding data variable, with a flag value of 0 representing data which are presumed to be of sufficient quality. Larger values of the flag generally correspond to lower quality data, though this isn’t always the case.

For example, consider a variable array with values

1 2 6 5 4 3 6 5 4 3 2 1 4 5 6 7 7 6 5 3 2

and its corresponding flag with values

0 0 0 0 1 1 0 1 1 1 2 2 1 0 0 0 0 0 0 0 0

To understand the meaning of these flag values, we can look at the flag_values and flag_meanings attributes of the flag variable, which may look like

• flag_meanings: data_good minor_data_quality_issue major_data_quality_issue

• flag_values: 0b 1b 2b

We can see that there are three different flag meanings and three different flag values, and can deduce that a flag value of 0 indicates the data are considered good, a flag value of 1 indicates a minor data quality issue, and a flag value of 2 indicates a major data quality issue. A user may choose, for example, to eliminate data with a major quality issue. To do this, they would simply mask/nan the variable whereever the flag variable has a value of 2, leaving the variable array as

1 2 6 5 4 3 6 5 4 3 - - 4 5 6 7 7 6 5 3 2.

Value-based flags will have the same dimensions as their associated variable, and the following variable attributes:

• _FillValue: -128b

• standard_name: ‘status_flag’ if the associated variable has no standard name, otherwise ‘<variable_standard_name> status_flag’

• long_name: Flag for <variable_name>

• flag_values: An array of the values that the flag variable can take. Typically runs from 0 to <length of flag_meanings> - 1.

• flag_meanings: A space separated string of the meanings of each of the values in flag_values.

Bitmask flags

While the value-based flags map the values of an array to a single meaning, bitmask flags allow the representation of a boolean array for every flag_meaning. This is done by mapping each flag meaning to an increasing power of 2, which allows the representation of every possible state of every meaning using values from 1 to \(2^{\text{num. flags}-1}\). A value of 0 indicates that no flags are set, and is set as a fill value. In order to a bitmask flag it must first be unpacked. This adds to the complexity of using the flag, but makes flags much more powerful, so most variables in the FAAM core data product use bitmask flags.

For example, consider a variable array with values

1 2 6 5 4 3 6 5 4 3 2 1 4 5 6 7 7 6 5 3 2

and its corresponding flag with values

1 1 3 3 2 2 4 4 4 4 6 6 6 6 8 8 5 5 3 3 1

To understand the meaning of these flag values, we can look at the flag_masks and flag_meanings attributes of the flag variable, which may look like

• flag_meanings: aircraft_on_ground flow_out_of_range temp_out_of_range data_out_of_bounds

• flag_masks: 1b 2b 4b 8b

There are four meanings, with each associated with a value of \(2^n\) with \(n\) taking the four values 0, 1, 2, 3. In the FAAM core data, flag values are guaranteed to be increasing powers of 2, thus the flag array can be unpacked simply by progressively right-bitshifting the flag array, and taking the result modulo 2. In python, this can be achieved with the following code:

# Note that we don't need to worry about using the flag_masks attribute, as it
# is guaranteed to be powers of 2 from 1 to 2^(n-1)
unpacked = {}
for i, meaning in enumerate(flag_var.flag_meanings.split()):
    unpacked[meaning] = (flag_data >> i) % 2

this would leave us with the following in unpacked:

{
    aircraft_on_ground: array([1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1]),
    flow_out_of_range: array([0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0]),
    temp_out_of_range: array([0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0]),
    data_out_of_bounds: array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0])
}

Bitmask flags will have the same dimensions as their associated variable, and the following variable attributes:

• _FillValue: 0b

• standard_name: ‘status_flag’ if the associated variable has no standard name, otherwise ‘<variable_standard_name> status_flag’

• long_name: Flag for <variable_name>

• valid_range: The valid range of values in the flag variable array. Should be 1b, 2^(<number of flag_meanings>) - 1

• flag_masks: An array of the values that the flag variable can take, which will runs from 1 to 2^(<number of flag_meanings> - 1).

• flag_meanings: A space separated string of the meanings of each of the values in flag_values.