Opened 9 years ago

Last modified 9 years ago

#113 new task

Eagle/Hawk spectra over water have a "bump" at ~970nm

Reported by: benj Owned by: benj
Priority: immediate Milestone:
Component: Data collection Keywords:
Cc: mggr Other processors:

Description (last modified by benj)

Eagle and Hawk spectra over water both seem to have an unexplained "bump" at around 970nm (upper end of Eagle's range, lower end of Hawk's). Water IR reflectance shouldn't have this bump, should just be black (exponential decay curve to very low values).

For graph below, red and pink lines are Eagle and Hawk respectively from a Caligeo-processed level 1 file, green and blue lines are Eagle and Hawk respectively from an azspec-processed level 1 file (spikes in azspec SWIR are being dealt with in ticket #110). It can be seen that Eagle starts to rise slightly at ~960nm and Hawk is far too high until about 1140nm (if not higher - hard to tell)

Azspec and caligeo output for Eagle and Hawk over water (8px average, Nigg Bay line 3, level 1 data)

Also (may be a separate issue), there is a difference between azspec and Caligeo processed data at the short-wave end of both sensors. This may be due to handling of smear correction, but since Hawk's got the larger error and that's supposedly not smear corrected, possibly not. Note that Azspec is slightly higher than Caligeo for Eagle and lower for Hawk. In both graphs below, Azspec is red and Caligeo is green.

Eagle:

azspec and caligeo processed eagle spectra over land

Hawk:

azspec and caligeo processed hawk data over land

Attachments (6)

azvscali_water.jpg (95.2 KB) - added by benj 9 years ago.
Azspec and caligeo output for Eagle and Hawk over water (8px average, Nigg Bay line 3, level 1 data)
azvscali_eagleland.jpg (73.0 KB) - added by benj 9 years ago.
azspec and caligeo processed eagle spectra over land
azvscali_hawkland.jpg (75.5 KB) - added by benj 9 years ago.
azspec and caligeo processed hawk data over land
nigg_specim_deep_water.jpg (22.6 KB) - added by mggr 9 years ago.
Specim spectra over deep water at Nigg Bay
eagle_calibration_stats.png (4.7 KB) - added by mggr 9 years ago.
hawk_calibration_stats.png (4.0 KB) - added by mggr 9 years ago.

Download all attachments as: .zip

Change History (13)

Changed 9 years ago by benj

Azspec and caligeo output for Eagle and Hawk over water (8px average, Nigg Bay line 3, level 1 data)

comment:1 Changed 9 years ago by benj

  • Description modified (diff)

comment:2 Changed 9 years ago by mggr

  • Description modified (diff)

Tweak to description.

Note also the divergence of the spectra for the two processing systems - azspec appears to be better. Perhaps the bump is due in part to smear correction and in part due to poor calibration at the edge of the ccd?

Changed 9 years ago by benj

azspec and caligeo processed eagle spectra over land

Changed 9 years ago by benj

azspec and caligeo processed hawk data over land

comment:3 Changed 9 years ago by benj

  • Description modified (diff)

comment:4 Changed 9 years ago by benj

  • Description modified (diff)

comment:5 Changed 9 years ago by benj

  • Description modified (diff)

Changed 9 years ago by mggr

Specim spectra over deep water at Nigg Bay

comment:6 Changed 9 years ago by mggr

Interestingly, this plot shows much lower Hawk values, although Eagle is still too high. Note the Hawk output is very spikey though - possibly indicating high amplification in the calibration phase / low sensitivity in the CCD. If so, this would mean it'd be easy to get a bump in Hawk too purely from noise.

Specim spectra over deep water at Nigg Bay

Changed 9 years ago by mggr

Changed 9 years ago by mggr

comment:7 Changed 9 years ago by mggr

Eagle min/mean/max plot of calibration values:


Note increasing magnitude of calibration values at the high and low wavelengths, indicating decreasing sensitivity and higher susceptibility to noise.

Hawk min/mean/max plot of calibration values:

Similar decrease in sensitivity as it reaches the 1000nm range. Also a frightening result around ~2150nm - that needs investigating.

Note: See TracTickets for help on using tickets.