# ACE_FTS_L2_iso

## Variables

The table below lists the variables that are present in the HARP product that results from an ingestion of `ACE_FTS_L2_iso` data.

field name | type | dimensions | unit | description
--- | --- | --- | --- | ---
datetime | double | {time} | [seconds since 2000-01-01] | date and time of occultation 30 km geometric tangent point
datetime_start | double | {time} | [seconds since 2000-01-01] | date and time of start of measurement
datetime_stop | double | {time} | [seconds since 2000-01-01] | date and time of end of measurement
orbit_index | int32 |  |  | absolute orbit number
latitude | double | {vertical} | [degree_north] | latitude of 30 km geometric tangent point for occultation
longitude | double | {vertical} | [degree_east] | longitude of 30 km geometric tangent point for occultation
altitude | double | {vertical} | [km] | tangent altitude grid for retrieved parameters and species
temperature | double | {vertical} | [K] | temperature
pressure | double | {vertical} | [hPa] | pressure
number_density | double | {vertical} | [cm^-3] | atmospheric density
H2O_181_volume_mixing_ratio | double | {vertical} | [ppmv] | volume mixing ratio for H2O_181
H2O_181_volume_mixing_ratio_uncertainty | double | {vertical} | [ppmv] | volume mixing ratio uncertainty for H2O_181. If this value is -888 the vmr was not retrieved but obtained by scaling the a priori value
H2O_171_volume_mixing_ratio | double | {vertical} | [ppmv] | volume mixing ratio for H2O_171
H2O_171_volume_mixing_ratio_uncertainty | double | {vertical} | [ppmv] | volume mixing ratio uncertainty for H2O_171. If this value is -888 the vmr was not retrieved but obtained by scaling the a priori value
H2O_162_volume_mixing_ratio | double | {vertical} | [ppmv] | volume mixing ratio for H2O_162
H2O_162_volume_mixing_ratio_uncertainty | double | {vertical} | [ppmv] | volume mixing ratio uncertainty for H2O_162. If this value is -888 the vmr was not retrieved but obtained by scaling the a priori value
CH4_311_volume_mixing_ratio | double | {vertical} | [ppmv] | volume mixing ratio for CH4_311
CH4_311_volume_mixing_ratio_uncertainty | double | {vertical} | [ppmv] | volume mixing ratio uncertainty for CH4_311. If this value is -888 the vmr was not retrieved but obtained by scaling the a priori value
CH4_212_volume_mixing_ratio | double | {vertical} | [ppmv] | volume mixing ratio for CH4_212
CH4_212_volume_mixing_ratio_uncertainty | double | {vertical} | [ppmv] | volume mixing ratio uncertainty for CH4_212. If this value is -888 the vmr was not retrieved but obtained by scaling the a priori value
index | int32 | {time} |  | zero-based index of the sample within the source product

## Mapping description

The table below details where and how each variable was retrieved from the input product.

field name | mapping description
--- | ---
datetime | path | /date
description | date field from header section converted to seconds since 2000-01-01
datetime_start | path | /start_time
description | start_time field from header section converted to seconds since 2000-01-01
datetime_stop | path | /end_time
description | end_time field from header section converted to seconds since 2000-01-01
orbit_index | description | extracted from the filename (assuming ssXXXXX… or srXXXXX… format); set to 0 if extraction of the value was not possible
latitude | path | /latitude
description | latitude field from header section
longitude | path | /longitude
description | longitude field from header section
altitude | path | /data section/z
temperature | path | /data section/T
pressure | path | /data section/P (atm)
number_density | path | /data section/dens
H2O_181_volume_mixing_ratio | path | /data section/H2O_181
H2O_181_volume_mixing_ratio_uncertainty | path | /data section/H2O_181_err
H2O_171_volume_mixing_ratio | path | /data section/H2O_171
H2O_171_volume_mixing_ratio_uncertainty | path | /data section/H2O_171_err
H2O_162_volume_mixing_ratio | path | /data section/H2O_162
H2O_162_volume_mixing_ratio_uncertainty | path | /data section/H2O_162_err
CH4_311_volume_mixing_ratio | path | /data section/CH4_311
CH4_311_volume_mixing_ratio_uncertainty | path | /data section/CH4_311_err
CH4_212_volume_mixing_ratio | path | /data section/CH4_212
CH4_212_volume_mixing_ratio_uncertainty | path | /data section/CH4_212_err