TIMED SEE

SEE Level 4 XPS Modeled Solar Irradiance Data

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Detailed Level 4 XPS Model Description

README_SEE_XPS_L4_011.TXT - information for using XPS_L4 data

The SEE XPS Level 4 data are derived from the XPS Level 1 data products. The XPS Level 4 processing algorithm uses reference CHIANTI spectral models to generate a higher spectral resolution (0.1 nm) estimate of the solar XUV irradiance by scaling the model reference spectra to match the XPS photometer currents (signal). The CHIANTI Quiet Sun (QS) spectrum and Active Region (AR) spectrum are used with a scaling of the AR spectrum to match the minimum signal on each day, and then a CHIANTI isothermal flare spectrum is scaled to match the signal above the daily minimum signal. The flare temperature is determined from the ratio of the GOES XRS 0.1-0.8 nm irradiance to the GOES XRS 0.05-0.4 nm irradiance. These scaling factors, flare temperature, and resulting model spectrum in the 0-40 nm range in 0.1 nm intervals are in the XPS Level 4 data product for every measurement made by XPS photometer #1 or #2 (0.1-7 nm band).

A SEE XPS Level 4 data product is produced for each UT day, and these daily products are also merged into three different full mission data files:

  1. daily averages (24-hour)
  2. orbit averages (3-min about every 97 min)
  3. 1-minute averages (but with only about 3% duty cycle)
The XPS Level 4 result in 0.1 nm intervals is also compressed into 1-nm intervals for use in the SEE Level 3 and Level 3A data products.

On-orbit instrument characterization is an ongoing effort, and the SEE team checks photometer degradation using redundant channels and underflight calibration rockets whose payload includes TIMED SEE prototype instruments.

The accuracy of the XPS Level 1 irradiance is 12%-26%, photometer dependent. There is additional uncertainty for applying the spectral model for the XPS Level 4 irradiances, and this estimated accuracy is 30% for the integrated XUV irradiance. The spectral distribution in the XPS Level 4 is from the CHIANTI model and not from direct measurements from XPS, a set of broadband photometers. The spectral distribution above 27 nm has been validated with the TIMED SEE EGS (27-190 nm, 0.4 nm resolution) measurements, so there is good confidence in the spectral distribution shortward of 27 nm.

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Reading the Data with IDL

With read_netcdf.pro individual data files may be read using an IDL command such as:

read_netcdf,'xps_L4_2002022_011.ncdf',d,att
The data will then reside in the returned structure "d", with each tag in the structure defined in the attributes array "att". The wavelength for the model flux range from 0-40.0 nm in 0.1 nm intervals with 0.05 nm centers.

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SEE Level 4 XPS Software

  • TIMED-SEE NetCDF README - Described IDL source code and gives examples using read_netcdf.pro and write_netcdf.pro
  • read_netcdf.pro - IDL procedure for reading NetCDF files as a structure
  • write_netcdf.pro - IDL procedure for writing a data structure (or array of structures) to a NetCDF file
  • plot_xps4.pro - IDL procedure for plotting a time series of SEE XPS Level 4 data.
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SEE Level 4 XPS Model Solar Irradiance Data Format

Each data file contains an array of structures with as many elements as valid integration from XPS channel 1.

L4_XPS_DATA     STRUCT    = ->  Array[31]

Each L4_XPS_DATA structure has the following form:

** Structure <30af48>, 14 tags, length=1652, data length=1650, refs=1:
DATE LONG 2002022
TIME FLOAT 1130.15
XPS_QS FLOAT 1.00000
XPS_AR FLOAT 0.211338
XPS_FLARE FLOAT -0.00110218
GOES_QS FLOAT 1.00000
GOES_AR FLOAT 0.0229278
GOES_FLARE FLOAT 0.0451341
FMTEMP FLOAT 6.53379
FMINDEX INT 11
FMWEIGHT FLOAT 0.331066
ERR_ABS FLOAT 0.759908
ERR_MEAS FLOAT 0.0140824
MODELFLUX FLOAT Array[400]

NetCDF file attributes for day 2002022

GLOBAL:

Title = SEE XPS Level 4 Data Product - 1 nm spectrum
Source = SEE POC at LASP / CU
Mission = TIMED
Data_product_type = XPS Level 4
Data_product_version = 011
Data_product_revision = 01
Product_format_version = 001
Software_version = 11.01
Software_name = write_netCDF.pro called from xps_temp_model.pro
Calibration_version = 11.01
Description = Spectral XUV irradiance model based on calibrated XPS data and flare plasma temperature derived from GOES XRS
History = 06/28/06 Don Woodraska Initial creation.
Filename = /titus/timed/testing/data/science_dp/level4/xps_L4_2002022_011.ncdf
Date_generated = Tue Aug 21 08:44:50 2012
DATE:
Units = YYYYDOY
Description = Year and day-of-year for the observation
TIME:
Units = Seconds
Description = Seconds of day for the center of the observation
XPS_QS:
Units = None
Description = Daily quiet-sun scale factor derived from XPS-1,-2 daily minimum (usually 1.0)
XPS_AR:
Units = None
Description = Daily active-region scale factor derived from XPS-1,-2 daily minimum (usually < 0.1)
XPS_FLARE:
Units = None
Description = Flare scale factor for each XPS-1,-2 integration with large numbers (> 2) indicating modest and large flares
GOES_QS:
Units = None
Description = Daily quiet-sun scale factor derived from GOES XRS-B daily minimum
GOES_AR:
Units = None
Description = Daily active-region scale factor derived from GOES XRS-B daily minimum
GOES_FLARE:
Units = None
Description = Flare scale factor for each GOES XRS-B integration with large numbers (> 2) indicating modest and large flares
FMTEMP:
Units = Log10(K)
Description = Flare model temperature derived from ratio of GOES XRS-B to XRS-A
FMINDEX:
Units = None
Description = Index into flare model table (indicating the temperature in model below the "fmtemp" value)
FMWEIGHT:
Units = None
Description = Weight parameter for the flare model at the "fmindex" temperature
ERR_ABS:
Units = Fractional
Description = Total combined standard uncertainty of the "modelflux" irradiance results (accuracy)
ERR_MEAS:
Units = Fractional
Description = Count-rate based combined standard uncertainty of the XPS-1,-2 measurement (precision)
MODELFLUX:
Units = W / m^2 / nm
Description = Array of solar irradiances in 0.1 nm bins from 0 to 40 nm (on 0.05 nm centers) based on scaling the Chianti spectral irradiance models using the calibrated XPS data and flare plasma temperature derived from GOES XRS
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      NASA SEE TIMED LASP

Revised: November 2007
+ Questions or comments?