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Aurora Integrating Nephelometer

The Aurora is an integrating nephelometer used for measuring light scattering properties of aerosols at multiple wavelengths.

AeroViz.rawDataReader.script.Aurora.Reader 

Reader(*args, **kwargs)

Bases: AbstractReader

Aurora Integrating Nephelometer Data Reader

A specialized reader for Aurora nephelometer data files, which measure aerosol light scattering properties at multiple wavelengths.

See docs/api/instruments/nephelometers/Aurora.md for usage and docs/guide/reader-reference.md for the file layout, status codes and QC rules.

Attributes

nam class-attribute instance-attribute 

nam = 'Aurora'

SCAT_COLUMNS class-attribute instance-attribute 

SCAT_COLUMNS = ['B', 'G', 'R', 'BB', 'BG', 'BR']

CAL_COLUMNS class-attribute instance-attribute 

CAL_COLUMNS = ['sca_550', 'SAE']

MIN_SCAT_VALUE class-attribute instance-attribute 

MIN_SCAT_VALUE = 0

MAX_SCAT_VALUE class-attribute instance-attribute 

MAX_SCAT_VALUE = 2000

STATUS_COLUMN class-attribute instance-attribute 

STATUS_COLUMN = 'Status'

STATUS_COLUMNS class-attribute instance-attribute 

STATUS_COLUMNS = ['Status', 'status', 'Error', 'error', 'Flag', 'flag', 'S1']

STATUS_OK class-attribute instance-attribute 

STATUS_OK = 0

Methods:

_raw_reader 

_raw_reader(file)

Read and parse raw Aurora nephelometer data files.

Returns all columns from the raw file. Column selection is deferred to _QC() and _process() stages.

_QC 

_QC(_df)

Perform quality control on Aurora nephelometer raw data.

QC Rules Applied (raw data only)
  1. Status Error : Non-zero status code indicates instrument error
  2. No Data : All scattering columns are NaN
  3. Invalid Scat Value: Scattering coefficient outside 0-2000 Mm^-1
  4. Invalid Scat Rel. : Wavelength dependence violation (B < G < R)
  5. Insufficient : Less than 50% hourly data completeness

Note: SAE calculation is done in _process() after QC.

_process 

_process(_df)

Calculate scattering coefficients and SAE.

Processing Steps
  1. Calculate scattering coefficient at 550nm
  2. Calculate SAE (Scattering Ångström Exponent)

Parameters:

Name Type Description Default
_df DataFrame

Quality-controlled DataFrame with scattering columns and QC_Flag

 required

Returns:

Type Description
DataFrame

DataFrame with sca_550, SAE, and updated QC_Flag

Raw format

  • File pattern: *.csv
  • Native frequency: 1min (config fallback; the grid actually used is detected per file and reported as df.attrs['raw_freq'])
  • Timestamp column: the first column (Data_Time on the production Ecotech export, Date / time local on others), used as the index and coerced to datetime; Raw_Data_Time is dropped as redundant
  • Column naming conventions (all are rewritten to the standard names below):
    • 0°σspB, 0°σspG, 0°σspR → B, G, R; 90°σspB, 90°σspG, 90°σspR → BB, BG, BR
    • Blue, Green, Red → B, G, R; B_Blue, B_Green, B_Red → BB, BG, BR
    • the production CSV layout is Data_Time, Raw_Data_Time, Red, Green, Blue, B_Red, B_Green, B_Blue, T1, T2, RH, P, S1, S2
  • Every other source column (T1, T2, RH, P, S2, …) is kept

Parse recipe

  • read_csv(low_memory=False, index_col=0); column names are stripped of surrounding spaces before the aliases are applied
  • The first column found among Status, status, Error, error, Flag, flag, S1 is renamed to Status
  • Rows with an unparseable or duplicated timestamp are dropped

Measurement parameters

The Aurora provides measurements at three wavelengths (Ecotech Aurora 3000 bands, as used by the SAE / sca_550 computation):

Column Wavelength Description
B 450 nm Total scattering (blue)
G 525 nm Total scattering (green)
R 635 nm Total scattering (red)
BB 450 nm Backscattering (blue)
BG 525 nm Backscattering (green)
BR 635 nm Backscattering (red)

Status & error codes

Column Status (after the rename above), mode numeric with ok_value=0 (see status modes): a row is an error when the status is not 0 and not NaN. Only 0 (normal operation, ambient sampling) is defined; there is no register table, so df.attrs['status_conditions'] is not produced. A missing status column is logged by check_status_columns and leaves the rule inert.

S1 is the status. The production CSV contains none of the obvious status names — the status is S1. Evidence from 120 one-minute scans (2025-01-01): S1 ∈ {0, 4}; the 17 rows with S1 == 4 are contiguous (00:06–00:22) and their scattering decays 185 → 0.78 Mm⁻¹ while S1 == 0 rows average 193 Mm⁻¹ — the signature of the zero/span check, where the instrument samples filtered air. Those rows pass the 0–2000 range check, so before S1 was recognised they were averaged into ambient means: on that fixture, dropping them raises the green-channel mean from 170.8 to 193.2 Mm⁻¹, a 13 % low bias removed.

S2 moves in step (0x07 while ambient, 0xAB/0xA8 during the check) and is evidently a bitfield. Its bits are not decoded — no manual to hand, and guessing bit meanings would be worse than leaving it as data. It is carried through to the output unchanged.

To treat a code as OK (for example if a site wants the zero/span rows kept), whitelist its numeric value:

RawDataReader('Aurora', path, ignored_status_errors=[4])

QC rules

Rule Condition Severity
Status Error Status ≠ 0 and not NaN (see above) error
No Data all six scattering columns (B, G, R, BB, BG, BR) are NaN error
Invalid Scat Value any scattering column ≤ 0 or > 2 000 Mm⁻¹ (MIN_SCAT_VALUE / MAX_SCAT_VALUE) error
Invalid Scat Rel B < G and G < R — inverted wavelength dependence (physically blue should scatter most) error
Insufficient an hour holds < 50 % of the points it could have held at the detected frequency (edge hours scaled by coverage) advisory (WARNING) — recorded, data kept

SAE and sca_550 are computed in _process after QC, not checked by a rule.

Output

_process runs _scaCoe on B, G, R (using the 450/525/635 nm bands) to add sca_550 and SAE, then re-attaches every non-scattering column.

Column Unit Description
B, G, R Mm⁻¹ Total scattering coefficients
BB, BG, BR Mm⁻¹ Backscattering coefficients
sca_550 Mm⁻¹ Scattering at 550nm
SAE - Scattering Angstrom Exponent (positive by convention)
T1, T2, RH, P, Status (from S1), S2, … as exported All other source columns, carried through unchanged

Files written per read are listed in RawDataReader Reference §1.

Notes

  • Provides real-time measurement of aerosol scattering
  • Same QC rules as NEPH nephelometer
  • Wavelength dependence follows Rayleigh scattering principle