2017-5-02 0.7 version 0.7

# HAYABUSA2 Optical Navigation Camera (ONC)

## Instrument Overview

The optical navigation camera (ONC) system onboard the Hayabusa2 spacecraft consists of one telescopic camera (T) and two wide-angle cameras (W1 and W2).

The ONC-T is a telescopic camera with seven band-pass filters in the visible and near-infrared range. These filters are placed on a wheel, which rotates to put a selected filter for different observations, enabling multiband imaging.

The main objective of this instrument is to optically navigate the spacecraft to asteroid Ryugu (1999 JU3) and to conduct muti-band mapping the asteroid for choosing touchdown candidate sites and understanding the nature of this asteroid.

Details on preflight calibration results of ONC-T are given by Kameda et al. (2016) those for ONC-W1 and W2 and inflight calibrations for the three cameras are given by Suzuki et al. (2017), respectively.

## Definition of Product Level

• l2a.... Raw images in FITS format (16 bit integer))
• l2b.... Images after radiometric correction in FITS format (32 bit float) (in prepa ration)
• l2c.... Distortion corrected images in FITS format (32-bit float) (in prep aration)
• l2d.... Photometrically corrected reflectance images in FITS format (32-bi t float) (in preparation)
• l2e.... Co-registered reflectance multi-band images in FITS format (32-bit float) (in preparation)
• l3.... Mosaiced global reflectance multi-band images in FITS format (32-b it float) (in preparation)

## File Naming Convention

• hyb2_onc_yymmdd_hhmmss_CBT_ldx(x).fit
•  Symbols Meaning yymmdd_hhmmss Expoture start time in UTC. CB Camera type {w1, w2, t+band{u:ul, i:WIDE, v:v, w:w, x:x, n:Na, p:p,b:b}} T Image Type {f:mainframe(1024x1024), b:opticalBlack(16x1024x2(on both sides))} ldx(x) Product level. e.g., l2a, l2b. Additional character is added to describe minor version of the higher product such as l2de).

## Imaging Condition

The details of the imaging condition are described in FITS header of each image file or a extracted FITS header in text format (example) and can be previewed from the link "hdr" below thumbnail images in the product summary pages.

Important FITS keywords are listed in below.

• CNTTYPE : Type of data content.
• EXPOSURE : Exposure time [sec]
• BITDEPTH : Bit pixel depth actually used 12/10/8. (not ready yet)
• SMEARCR : Smear correction {NON/ONBOARD/GROUND}.
• Smear correction is conducted by subtracting a image taken at expoture time of 0 sec from a target image.
• P_CMPSTY: Image compression style: RAW_DATA/LOSSLES/LOSSY
• P_CMPTYP: Image compression type: RAW_DATA/STARPIXEL
• S_DISTHR : Distance between HYB2 and Ryugu [km]
• S_DISTHE : Distance between HYB2 and Earth [km]
• S_DISTHS : Distance between HYB2 and Sun [km]
• S_DISTRS : Distance between Ryugu and Sun [km]

## Data Processing tools

• Visualization: Please use visualization tools supporting FITS format, such as DS9 or GIMP
• Analysis: Please use libraies supporing FITS format operations as listed below .

## Calibration (in preparation)

### (1) Alignment Offset

The alighment offset (the deviation of the optical axis from the center of the image is also included) is summarized as table below (see Suzuki et al. (2017) for details) .

 W1 W2 T dx [pixel] -3.7 +/- 1.0 0(<1) 11.4 +/- 0.6 dy [pixel] -3.2 +/- 1.0 0(<1) -22.0 +/- 0.7

### (2) Distortion Correction

Suppose the pixel at the position (x, y) in the image is projected to the point (x', y') after the distortion correction (the origin is defined to be the center of the image). The distance of the pixel from the center of the image is denoted by $r =\sqrt{\mathrm{x2+y2}}$.

The projection relation of the point with the distance r to the point with the distance r' is given by

$r\text{'} = L$1 r + L2 r3+L3 r5, (1)

where L1, L2, and L3 are parameters for distortion correction defined for each camera. Then the pixel positions without distortion is calculated by the following equation (2):

$x\text{'}= \left(r\text{'}/r\right)x , y\text{'}= \left(r\text{'}/r\right)y$. (2)

The parameters in the above equations (1) and (2) obtained for W1, W2 and T are listed in table below. The details of the calibration using the star-field images are described in the paper by Suzuki et al. (2017).

 W1 W2 T L1 1.027 1.014 1 L2 3.219E-7 2.933E-7 -9.28E-9 L3 -1.762E-13 -1.384E-13 0 RMS Error [pixels] (after correction) 0.6 0.5 0.16