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Data Quality Summary for the CALIPSO Versions 2.00 and 2.01 IIR Level 1 Data Products


Last Updated: October 09, 2020



Data Version: 2.00     Data Version: 2.01
Data Release Date: July 12, 2017     Data Release Date: October 01, 2020
Data Date Range: June 13, 2006 to September 30, 2020     Data Date Range: October 1, 2020 to present

10-09-2020: A minor version bump (+0.01) has been applied to all CALIPSO data products due to a required upgrade to the operating system on the CALIPSO production cluster. All algorithms were re-compiled to process in this new environment with no change to the underlying science algorithms or inputs.

The brightness temperature differences between similar channels of IIR (Version 1 data) and MODIS (Collection 5 data) have been monitored since launch. These inter-comparisons have been further assessed by directly comparing each IIR and MODIS channel with radiative transfer simulations in clear sky conditions using meteorological profiles from reanalyses. In the tropics, the agreement with MODIS is better than 0.05 K for IIR channels 8.65 μm and 10.6 μm, and is within 0.26 K for IIR channel 12.05 μm. No drift is evidenced for any of the IIR channels: values are smaller than ± 0.004 K/year.

However, in Version 1, a striping effect as well as residual biases with respect to MODIS were occurring in the northern hemisphere, mostly north of 30°N, at season-dependent latitudes. These effects were caused by calibration drifts synchronized with the elapsed time since the night-to-day transition. Two distinct sets of correction coefficients were implemented in the Version 2 algorithm:

  • The first is an equalization correction, which is applied to about half of each individual image with respect to the other part of the image.
  • The second set of coefficients corrects overall radiometric biases that affected the whole image.

Figure 1.

Figure 1: IIR 10.6 μm-12.05 μm inter-channel brightness temperature difference during the nighttime descending portion of an orbit between 48°N and 41°N in June 2008. Top: Version 1; Bottom: Version 2. The arrows point to some of the darker stripes seen periodically in version 1. This striping effect seen in Version 1 is significantly attenuated in Version 2.


Figure 2.

Figure 2: IIR 8.65 μm-12.05 μm inter-channel brightness temperature difference during the nighttime descending portion of an orbit between 48°N and 41°N in June 2008. Top: Version 1; Bottom: Version 2. The arrows point to some of the darker stripes seen periodically in version 1. This striping effect seen in Version 1 is significantly attenuated in Version 2.


In Version 1, residual IIR calibration biases were clearly evident at 30-60°N in June and July, where the IIR-MODIS brightness temperature differences were on average larger by 0.2 K at 8.65 μm and by 0.4 K at 10.6 and 12.05 μm in the nighttime descending portion of each orbit than in the daytime ascending portion (Figure 3, left). With the refined Version 2 calibration (Figure 3, right), these differences are substantially reduced.

Figure 3.

Figure 3: Daily averaged brightness temperature differences between each IIR channel and a radiatively similar MODIS-Aqua band during 2008 (blue: night only; red: day only, black: day and night). Analysis applied to collocated oceanic pixels in the 30°-60°N latitude band and in the 280-290 K brightness temperature range. Top, middle and bottom panels are for the three paired IIR/MODIS Collection 5 channels. Left and right are for Version 1 and Version 2, respectively.

Pixel Quality Index Change
In Version 2, the “Pixel Quality Index” has been completed to flag the pixels for which an equalization correction has been applied (see Data Product Catalog).

Change in conversion from raw data to calibrated radiances
In Version 2, the calibrated radiances are obtained by applying a scale factor of 0.001 to the raw data. This scale factor was 0.01 in Version 1 (see Data Product Catalog).



NASA
Last Updated: April 28, 2021
Curator: Charles R. Trepte
NASA Official: Charles R. Trepte

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