Friday, February 26, 2010

Spot Checking The Spot Check

Before I posted the results of the QA spot check described here, I first checked those results to make sure they were accurate. This post describes how I checked them.

Checking Binary Data
The Aqua Satellite AMSU Level 1B data comes in compressed binary form. You can view the data using HDFView, which is a tool created by the HDF Group. I used this tool to go in to the data files exactly as they were downloaded from NASA and look at the data. The screen shot to the left shows the values of Channel 4 QA that I reported. Any value other than zero means the channel failed QA. As you can see, all of Channel 4's readings failed. Channel 4 is labeled as "3" because the numbering in the viewer starts at zero rather than one.

Checking Text Data
HDFView is an HDF viewer, not an HDF-EOS viewer. And the Aqua AMSU Level 1B files are HDF-EOS files. This means HDFView can show you the HDF parts of the file, but not the EOS parts of the file. To look at the EOS data in the file, I converted it to text and opened it up in a text editor. Conversion to text was done by taking the original NASA data file and running it through ncdump with no arguments other than the file name to be converted.

The two screen shots below show samples of EOS data for two different files. You can see the file names as the titles to the window. Looking at the highlighted data, you can see the name of the data shown and its value. The data is NumBadData and the value for both files is 1350.

These types of checks were done on about 20 randomly selected files to ensure the errors being reported by the QA code were actually due to the data in the files, not due to bugs in the QA code itself.

Previous Articles In This Series:
NASA, UAH Notified Of QA Spot Check Findings
About The Aqua Satellite Project
UAH January Raw Data Spot Check
So, About That January UAH Anomaly
A Note On UAH's High January Temperature

UAH January Raw Data Spot Check
Looking At The Aqua Satellite Data

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