The line below is a link to a zipped file containing the 2014 Arctic Bidirectional Reflectance data:
The "readme" file on this page contains information on the format of the data in that link,
and the corresponding email below:
From Matt Linkswiler on 8/15/14
I have fixed the corrupt timestamp issue and reprocessed data. I zipped it back up and uploaded it to the same location as before:
ftp://atm.wff.nasa.gov/outgoing/preliminary_spectrometry_2014/
and the file is called:
2014_IceBridge_spectrometery_reprocessed.tgz
Let me know if anyone sees any further issues.
-Matt
Readme file for preliminary processing of "albedo" data product.
Background
This data set includes down-welling spectral irradiance coupled with up-welling spectral radiance, collected with an Ocean Optics USB4000 spectrometer. The down-welling irradiance was measured using a zenith-looking cosine corrector to view the sky with a 180-degree field of view. The up-welling radiance was measured using a nadir-looking cosine corrector to view the ice below the plane with a 180-degree field of view. Unfortunately, due to the installation constraints, the nadir-looking cosine corrector was installed immediately behind a 1"-thick acrylic window, and therefore had an actual field of view of slightly less than 180-degrees. Both cosine correctors were attached to the same fiber optic switch with 5-meter optical fiber. The spectrometer-end of the fiber optic switch connected to a bifurcated optical fiber which directed both optical paths into the USB4000 spectrometer.
The USB4000 spectrometer measures 3648 spectral channels from ~180nm to 880nm, with a 16-bit dynamic range. The integration time of the spectrometer was generally between 500ms and 1000ms to prevent the maximum signal from saturating. The integration time is fixed for each data file, and is specified in the file header.
When switching the spectrometer between viewing two significantly different targets, it was observed that the spectrometer would take a couple acquisitions to "settle" to an accurate measurement. In order to guarantee an accurate measurement, the fiber optic switch was actuated once, every five measurements. This produced five down-looking measurements, followed by five up-looking measurements. For the final data product, only the last of these five measurements was retained. The spectrometer ouput was split into two separate data files--one for the down-looking spectra, and one for the up-looking spectra.
In post-processing, the spectrometer data files were merged with an aircraft-attitude data file (from a VectorNav VN200 IMU) and a "sun angle" data file, which described the sun's azimuth and elevation angles for each point along the plane's trajectory. The merged data file incorporates the spectrometer raw output (counts) for each wavelength channel, plus the following data fields:
Year
Day_Of_Year
Seconds_Of_Day(UTC)
Latitude(deg)
Longitude(deg)
Aircraft_Altitude_Above_Ellipsoid(m)
Roll(deg)
Pitch(deg)
Heading(deg)
Sun_Azimuth(deg)
Sun_Elevation(deg)
We are interested to see whether this data product could be used to create an albedo data product for the IceBridge Project. Unfortunately, due to flying at high latitudes in the spring, the sun angle was usually very low (<30 degrees).
Feel free to contact us if you have any questions about the data set:
Matt Linkswiler (Matthew.A.Linkswiler@*.gov)
Alexey Chibisov (Alexey.V.Chibisov@*.gov)