  Hayabusa2 collected 5.4 g of samples from the asteroid (162173) Ryugu and
brought them back to Earth. Obtaining multiband images of these samples with
the spectral bands comparable to those used for remote-sensing observations is
important for characterizing the collected samples and examining how
representative the sample is compared with spacecraft observations of Ryugu as
a whole. In this study, we constructed a multiband microscopic camera system
that enables both visual multispectral imaging at 390 (ul), 475 (b), 550 (v),
590 (Na), 700 (w), and 850 nm (x), and three-dimensional (3D) shape
reconstruction of individual grain samples based on stereo imaging. The imaging
system yields the images of 4096 x 2160 pixels with the pixel resolution of
1.93 {\mu}m/pix and field of view of 7.9 x 4.2 mm. Our validation measurements
demonstrate that our multispectral imaging system, which observes the samples
with the spectral bands comparable to those on the telescopic optical
navigation camera (ONC-T) on Hayabusa2, yields reflectance spectra with a
relative error of 3% and a 3D model with an error of 5%. These results indicate
that the multiband imaging system with a 3D shape reconstruction capability
yields accurate spectral and shape data on the returned samples. Using this
instrument, we conducted multispectral measurements of two Ryugu samples
(grains in the dishes A3 and C1) acquired from two locations on the asteroid.
The average spectra of the measured Ryugu samples were flat and consistent with
the global averaged spectrum of Ryugu. The 550-nm band (v-band) reflectance of
the returned grains in the dishes was 2.4% on average, higher than that of the
global averaged spectrum of Ryugu observed with ONC-T. This apparent difference
could be because the returned grains have greater specular reflectance.
