COL 9(6), 061201(2011) CHINESE OPTICS LETTERS June 10, 2011
Modified adaptive algebraic tomographic reconstruction of
gas distribution from incomplete projection by a
two-wavelength absorption scheme
Ning Li (李李李 宁宁宁)
∗
and Chunsheng Weng (翁翁翁春春春生生生)
State Key Laboratory of Transient Physics, Nanjing University of Science and Technology, Nanjing 210094, China
∗
Corresp onding author: lining@mail.njust.edu.cn
Received November 22, 2010; accepted January 20, 2011; posted online April 29, 2011
A modified adaptive algebraic reconstruction technique (MAART) with an auto-adjustment relaxation
parameter and smo othness regularization is developed to reveal the tomographic reconstruction of H
2
O
distribution in combustion from incomplete projections. Determinations of relaxation parameter and
regularization factor are discussed with regard to the consideration of improvement in reconstruction
and reduction of computational burden. A two-wavelength scheme from tunable diode laser absorption
measurement, 7444.36 and 7185.59 cm
−1
, is used to simplify the nonlinear solution problem for obtaining
the tomographic distributions of concentration and temperature simultaneously. Results of calculations
demonstrate that MAART can perform the reconstruction results more efficiently with little complex
mo dification and much lower iterations as compared with the traditional algebraic reconstruction technique
(ART) or simultaneous iterative reconstruction technique (SIRT) methods. The stability of the algorithm
is studied by reconstruction from projections with random noise at different levels to demonstrate the
dep endence of reconstruction results on precise line-of-sight measurements.
OCIS codes: 120.0120, 110.0110, 300.0300.
doi: 10.3788/COL201109.061201.
The technology with tunable diode laser absorption spec-
troscopy shows great potential for application in the mea-
surement of gas concentration and temperature during
combustion
[1−4]
, as well as measurement of distribution
in the line-of-sight nonuniform-property flows
[5−7]
. The
tunable diode laser sensing is a technology that is quite
attractive from the perspective of practical applications
with regard to the robustness of the system, relative ease
of use, and reasonable cost. Fiber lasers can easily cover
the extended range of specific transitions for more num-
ber of species by the wavelength division multiplexing
(WDM) technique. However, the inherent characteristic
of tunable diode laser sensing makes it more difficult
to achieve spatially resolved measurements. The optical
scanning system and reconstruction algorithm need to
be considered for the reconstruction of the gas concen-
tration and temp erature distributions with reasonable
projections. Unlike the rotating computed tomography
(CT) employed in medical radiation dosimetry
[8]
, the
laser source and detector arrays with fixed positions are
designed to maintain the time resolution for dynamic
combustion measurement, and this leads to incomplete
projections from the limited optics arrangement.
Tomography reconstruction is a nonlinear optimization
problem, attributed to the nonlinear temperature depen-
dence on absorption coefficients. An increase in transi-
tions would be an effective way to extend the absorp-
tion information for better quality of reconstruction
[9]
.
Techniques of simulated annealing (SA) have been inves-
tigated for reconstruction of temperature and concentra-
tion from 20 projection locations with 10 wavelengths at
each location in the 10 × 10 grids. However, when the
number of limited projections is much lower than the
number of unknown variables, derivation of the solution
for an ill-posed matrix equation by similar methods be-
comes unfeasible. Algebraic methods have been shown
to provide better reconstructions from limited views, al-
beit with the disadvantage of a greater computational
burden. An algebraic reconstruction technique (ART)
has been discussed in gas tomography reconstruction
where a total of 400 projections were collected from
four beam platforms (a single platform was rotated to
produce a fan beam) to reconstruct the gas distribu-
tion in the 10 × 10 grids
[10]
. In this letter, we discuss
a modified adaptive algebraic reconstruction technique
(MAART), which introduces adaptive adjustment of re-
laxation parameters
[11]
and smoothness regularization
during the reconstruction pro cedure. This technique is
developed to reconstruct the distributions of concentra-
tion and temp erature simultaneously under incomplete
projections for fast computation and high quality.
A scanning geometry measurement of parallel laser-
detector pairs at multi-view with a fixed location was
investigated in the region of interest, which was divided
into 8 × 8 discretization grids. The projection views were
arranged equally in a range of 180
◦
with an angle interval
Fig. 1. Optical arrangement for multi-view parallel scanning
geometry ( V = 4, R= 8).
1671-7694/2011/061201(5) 061201-1
c
° 2011 Chinese Optics Letters