I obtained the spectral response function for PACE HARP2 from the website: https://oceancolor.gsfc.nasa.gov/data/pace/characterization/.
I have the following doubts:
1) In the rsr for each band, I understand that -99 represents a missing value, but what do negative values other than -99 signify?
2）What does the last column ‘GLAMR_power’ in the table refer to?
3) How to convert RSR into a dimensionless spectral response function with a total integral of 1?
Thank you for your time and assistance.
The spectral response Table of PACE HARP2 includes negative values
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Re: The spectral response Table of PACE HARP2 includes negative values
Hello, the following are the answers to your questions. Hope it helps.
1) Negative values other than –99
These are observed negatives that passed the initial filtering. If a value exceeded the 3-sigma uncertainty, it was retained as potentially real (even if negative). Values within 3-sigma were masked as likely random variation. This way, users can decide themselves whether to keep or ignore the negatives.
2) ‘GLAMR_power’ column
This records the power measured by the GLAMR reference detector during HARP2 acquisition. HARP2 counts were divided by this value to correct for source power fluctuations. It’s kept in the file so users can, if needed, reconstruct the original counts or apply their own corrections. It is not HARP2’s own radiometric measurement.
3) Converting RSR to unit-area (integral = 1)
The file does not provide area-normalized RSRs. Instead, each band (red, green, blue, NIR) has a peak normalization factor so that the maximum in-band response is 1. To normalize yourself:
(a) Apply the 3-sigma uncertainty filter (see #1).
(b) Divide by GLAMR_power (see #2).
(c) Divide by the appropriate band’s normalization factor (based on wavelength).
This peak-based normalization was chosen to simplify cross-talk evaluation (e.g., blue filter leakage into NIR). If you need a dimensionless SRF with integral = 1, you’ll need to apply your own area normalization over the wavelength range after these steps.
Guoqing
1) Negative values other than –99
These are observed negatives that passed the initial filtering. If a value exceeded the 3-sigma uncertainty, it was retained as potentially real (even if negative). Values within 3-sigma were masked as likely random variation. This way, users can decide themselves whether to keep or ignore the negatives.
2) ‘GLAMR_power’ column
This records the power measured by the GLAMR reference detector during HARP2 acquisition. HARP2 counts were divided by this value to correct for source power fluctuations. It’s kept in the file so users can, if needed, reconstruct the original counts or apply their own corrections. It is not HARP2’s own radiometric measurement.
3) Converting RSR to unit-area (integral = 1)
The file does not provide area-normalized RSRs. Instead, each band (red, green, blue, NIR) has a peak normalization factor so that the maximum in-band response is 1. To normalize yourself:
(a) Apply the 3-sigma uncertainty filter (see #1).
(b) Divide by GLAMR_power (see #2).
(c) Divide by the appropriate band’s normalization factor (based on wavelength).
This peak-based normalization was chosen to simplify cross-talk evaluation (e.g., blue filter leakage into NIR). If you need a dimensionless SRF with integral = 1, you’ll need to apply your own area normalization over the wavelength range after these steps.
Guoqing