International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August - 01 September 2012, Melbourne, Australia 
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large block comprising 21 strips are presented in chapter 4. The 
paper concludes with some observations for future work. 
2 SINGLE ORBIT STRIPS 
The workflow for a systematic bundle adjustment of the HRSC 
image data can be divided into four parts: image pre-processing, 
tie point matching, bundle adjustment and evaluation. In addi 
tion to the HRSC images, the nominal exterior orientation and 
the Mars Orbiter Laser Altimeter (MOLA) DTM are used as in 
put. The adjusted exterior orientation is the output (see Fig. 2). 
The use of standard parameters for each processing step allows to 
apply this workflow to the entire HRSC data set without manual 
intervention. The most relevant parameters are described in the 
following sections. 
1 L 
image pre-processing 
rectified, filtered images 
tie point matching 
tie point coordinates 
Figure 2: Workflow for systematic bundle adjustment of HRSC 
image data 
2.1 Image pre-processing 
The first step for the processing of single orbit strips is image 
pre-processing. In this step only the panchromatic channels of 
the HRSC images are used. Initially a low pass filter is applied 
to reduce image noise. A simple Gaussian with a 3x3 pixel filter 
matrix have shown good results and leads to a more robust tie 
point matching (Schmidt, 2008). 
Subsequently the nominal orientation data and the MOLA DTM 
are used for a pre-rectification of the image data (Seholten et al., 
2005). This step compensates scale differences and corrects non 
quadratic pixels. 
2.2 Tie point matching 
In the nadir image the tie points are arranged as a regular grid. 
Given the desired number of points (approx. 45.000) and the im 
age size a corresponding grid width is calculated. In contrast to an 
interest operator, the grid ensures a more regular distribution of 
the tie points. Tie point matching is carried out in the pre-rectified 
images. Depending on the image quality, the final number of suc 
cessfully matched tie points lies between 20.000 and 45.000. 
Each candidate point in the nadir channel image is matched with 
the other four panchromatic channels. Because of higher macro 
pixel size and consequently a lower resolution, the color channels 
are normally not used for photogrammetric processing. 
For image matching a pyramidal approach is used to take large 
parallaxes and imprecise nominal orientation values into account. 
As similarity measure a normalized cross correlation coefficient 
is employed. A 35x35 pixel correlation window is used. Subse 
quently the matching results arc optimized by multi-image least 
squares matching (Schmidt et al., 2008). 
2.3 Bundle adjustment 
In the next part of the processing chain a combined bundle ad 
justment is carried out using the image coordinates of the tie 
points, the MOLA DTM and the nominal exterior orientation val 
ues (Spiegel, 2007a). 
The used bundle adjustment method is based on the well known 
approach used in photogrammetry, by which the exterior orien 
tation is simultaneously determined for all images. In ease of 
HRSC the images are not acquired from individual view points 
but in a continuous motion. Thus, the exterior orientation must 
be modeled along the spacecrafts trajectory as a function of time. 
Three decades ago the concept of orientation points was proposed 
to solve this problem (Hofmann et al., 1982). Today, it is a com 
mon approach in the processing of multi-line sensor data. 
To fit the photogrammetrically determined 3D coordinates of a 
photogrammetric bundle block to a regional or global reference 
system, an adequate number of ground control points is normally 
used in aerial or spacebome photogrammetry. For areas with 
out ground control points available DTMs can be used to obtain 
an absolute fit (Strunz, 1993). On Mars the MOLA DTM pro 
vides the best global accuracy. Therefore, a combined bundle 
adjustment for HRSC image data and the MOLA DTM as con 
trol information was developed, implemented and tested (Spiegel, 
2007b). 
The general approach of the bundle adjustment is a nonlinear 
least-squares adjustment. This optimization aims to find the best 
set of unknown model parameters to explain the observations. For 
a combined adjustment of HRSC images and the MOLA DTM 
there are four types of observations: image coordinates, orienta 
tion parameters, unknown bias and drift parameters to compen 
sate systematic effects and DTM information. The four types 
of observation equations used in the bundle adjustment are de 
scribed in (Bostelmann and Heipke, 2011). 
The stochastic model of a bundle adjustment can be modified by 
changing the a priori standard deviation of a particular type of 
observation. This allows to handle observations as constants with 
cro = 0, as free unknowns with cro —> oo or as stochastic values 
with a cro of something in between. The strategy specially devel 
oped for HRSC data divides the bundle adjustment into two parts 
with different values for the stochastic model (Spiegel, 2007b). 
The image coordinates of the tie points are always introduced 
with an a priori standard deviation of <To, xy = 1 [im. 
In the first part only the nominal orientation parameters at the ori 
entation points and the tie points are introduced, but no drift and 
bias and no DTM information. The a priori standard deviation 
for the orientation is chosen as go,^k = 0.028gon for the atti 
tude and (To,xyz = 0.01m for the position. The latter considers 
the stable orbit of the spacecraft. This part optimizes the internal 
accuracy of the strip. 
In the second part observations for bias and drift are introduced 
with (To,bias,xyz = 1000m allowing a translation of the whole 
strip. A drift for the height component of the exterior orientation 
is permitted by setting cro,drift,z = 0.01m/imageline. For X 
and Y no drift is introduced. For the orientation angles neither