This program calibrates images from the Hayabusa 2 ONC-T instrument. The input image is corrected for the following, in order, during calibration:

• Step 1: Bias and dark current removal.
• Step 2: Uniformity (flat field) correction.
• Notes
• References

Step 1: Bias and dark current removal.

The signal level of ONC-T is determined by a combination of an electronic offset which defines the "zero" level of the analog-to-digital converter (the bias) as well as any additional signal due to thermal electrons (the dark current). With this instrument, the bias level depends largely on the electronics package (ONC-AE) and is only slightly affected by the instrument's CCD temperature. Therefore, the bias correction has been modeled as a function of the ONC-AE temperature. The dark current is modeled as a function of the ONC-T CCD temperature. The constants B₀, B₁ and B₂ were determined by fitting a quadratic polynomial to the data provided in Fig. 3 Bias level and AE temperature on page 22 of Preflight Calibration (S. Kameda et al.)

Step 2: Flat-field correction:

Performs a correction for pixel-to-pixel variation in CCD response and vignetting (reduction of image brightness near the periphery compared with the center). Flat-field images for all filters were acquired from JAXA's DARTS. The correction is accomplished by dividing each pixel of the output image by the corresponding pixel in the flat-field image.

Notes

1. Smear correction is not currently provided, as we do not have the readout time (charge-transfer period) for the instrument.
2. Similarly, since no radiance values could be found for the instrument filters, the output cannot be correctly converted to radiance or I/F.

References:

1. S. Kameda et al. "Preflight Calibration Test Results for Optical Navigation Camera Telescope (ONC-T) Onboard the Hayabusa2 Spacecraft". Space Sci Rev (2017) 208:17-31.