Opened 12 years ago

Closed 10 years ago

#106 closed task (invalid)

Hawk data very noisy in some bands

Reported by: benj Owned by: benj
Priority: alpha 5 Milestone:
Component: Data collection Keywords: Hawk noise
Cc: mggr Other processors:

Description (last modified by benj)

Some Hawk bands are noisy to the point of uselessness. For example band 71 (1403nm), raw data from Nigg Bay line 3 (attached)


Also see over-water spectrum produced in level 3 image:

Hawk 8-pixel average spectrum over water in Nigg Bay

Spectrum cannot really be used for anything much - there is no means of quality controlling the data

Data issue occurs over more than one flight, possibly there are sensor problems with some Hawk bands. See eg. Latera band 71, similar to Nigg Bay:

Hawk band 71 (line 1) raw data from Latera

Attachments (6)

hawk_raw_1403_nigg_bay_b3.png (143.8 KB) - added by benj 12 years ago.
hawk_l3_spectrum.png (3.3 KB) - added by benj 12 years ago.
Hawk 8-pixel average spectrum over water in Nigg Bay
hawk_raw_latera_b71.png (161.3 KB) - added by benj 12 years ago.
Hawk band 71 (line 1) raw data from Latera
h_raw_samepixelspectrum.png (6.0 KB) - added by benj 12 years ago.
8-pixel average over-water spectra from the same pixel on two different scan lines (raw data)
h_raw_diffpixelspectrum.png (6.2 KB) - added by benj 12 years ago.
Spectra from different pixels on the same scan line (8-pixel average, raw data)
noisy_hawk_bands.png (603.1 KB) - added by mggr 11 years ago.

Download all attachments as: .zip

Change History (14)

Changed 12 years ago by benj

comment:1 Changed 12 years ago by benj

  • Description modified (diff)
  • Owner changed from gaew to benj

Changed 12 years ago by benj

Hawk 8-pixel average spectrum over water in Nigg Bay

comment:2 Changed 12 years ago by benj

  • Description modified (diff)

Changed 12 years ago by benj

Hawk band 71 (line 1) raw data from Latera

comment:3 Changed 12 years ago by benj

  • Description modified (diff)

comment:4 Changed 12 years ago by benj

Phil Goy said that he thinks the noisy hawk bands might be because these bands coincide with water absorption maxima - water absorbs most of the signal, so the signal to noise ratio is low for these bands. He's a bit concerned about the spikes in the spectrum though - those aren't explained by water absorption and look more like sensor underflows. He's going to send the Hawk calibration data down for us to see if that does the same thing.

Changed 12 years ago by benj

8-pixel average over-water spectra from the same pixel on two different scan lines (raw data)

Changed 12 years ago by benj

Spectra from different pixels on the same scan line (8-pixel average, raw data)

comment:5 Changed 12 years ago by benj

Spikes seem to occur in the raw data as well as the processed data, though not as many (trying to integrate bad data may cause more spikes in the processed data). If you take two points in the raw data from the same pixel on different scan lines they both have very similar spikes, suggesting bad pixels for specific bands on the sensor itself, eg:

8-pixel average over-water spectra from the same pixel on two different scan lines (raw data)

If you take two points in the raw data from different pixels on the same scan line, they both have spikes but in different places:

Spectra from different pixels on the same scan line (8-pixel average, raw data)

This suggests that most spatial pixels on the Hawk CCD have at least one bad spectral pixel, but that it's not always the same spectral pixel that is bad.

comment:6 Changed 12 years ago by benj

Issues of azspec causing spiky spectra and bad pixels/calibration have been hived off to tickets #110 and #111 respectively - this ticket should now only be for noisy bands

Changed 11 years ago by mggr

comment:7 Changed 11 years ago by mggr

Better picture of noisy hawk bands - with azspec that's corrected for the spikes.

Band 87 (1504.61nm) vs band 71 (1403.66nm)

comment:8 Changed 10 years ago by benj

  • Resolution set to invalid
  • Status changed from new to closed

We pretty much concluded that this was just to do with water absorption - any band in a part of the spectrum where water absorbs a lot is noisy. Closing this ticket.

Note: See TracTickets for help on using tickets.