orientation of moms-02/d2 and moms-2p/priroda imagery

Ž .ISPRS Journal of Photogrammetry & Remote Sensing 54 1999 332–341

Orientation of MOMS-02rD2 and MOMS-2PrPRIRODAimagery 1

H. Ebner a,2, W. Kornus b, T. Ohlhof c,), E. Putz d

a ( )Chair for Photogrammetry and Remote Sensing, Technische UniÕersitat Munchen TUM , D-80290 Munich, Germany¨ ¨b ( )German Aerospace Center DLR e.V., Institute for Optoelectronics, PO Box 1116, D-82230 Wessling, Germany

c ( )Elektroniksystem-und Logistik ESG , System DeÕelopment, Reconnaissance and Remote Sensing Systems, PO Box 800 569,D-81605 Munich, Germany

d ( )Starkstrom-Anlagen-Gesellschaft SAG , Landshuter Str. 65, D-84030 Ergolding, .Germany

Received 13 June 1998; accepted 15 February 1999

Dedicated to Dr.-Ing. Otto Hofmann

Abstract

This paper deals with the orientation of three-line imagery which has been taken during the MOMS-02rD2 experiment inspring 1993, and during the MOMS-2PrPRIRODA mission since April 1996. The reconstruction of the image orientation isbased on a combined adjustment of the complete image, ground control, orbit and attitude information. The combinedadjustment makes use of the orientation point approach or the orbital constraints approach. In the second case, the bundleadjustment algorithm is supplemented by a rigorous dynamical modeling of the spacecraft motion. The results of thecombined adjustment using MOMS-02rD2 imagery and control information of orbit a75b are presented. Based on the

Ž .orientation point approach an empirical height accuracy of up to 4 m 0.3 pixel is obtained. In planimetry the empiricalŽ . Ž .accuracy is limited to about 10 m 0.7 pixel , since the ground control points GCP and check points could not be identified

in the imagery with the required accuracy. Computer simulations on MOMS-2PrPRIRODA image orientation based onrealistic input information have shown that good accuracies of the estimated exterior orientation parameters and object pointcoordinates can be obtained either with a single strip and a few precise GCP or even without ground control information, if a

Ž .block of several overlapping and crossing strips with high geometric strength qf60% is adjusted. q 1999 ElsevierScience B.V. All rights reserved.

Keywords: image orientation; Three-line CCD cameras; Bundle block adjustment; MOMS; Orbital constraints

) Corresponding author. Fax: q49-89-9216-2732; E-mail:[email protected]

1 Updated version of a paper presented at the ISPRS Congressin Vienna, 1996.

2 Tel.: q49-89-2892-2671; Fax: q49-89-280-9573; E-mail:[email protected].

1. Introduction

During the 2nd German Spacelab mission D2,successfully flown in AprilrMay 1993, the ModularOptoelectronic Multispectral Stereo Scanner MOMS-02 acquired digital high resolution, along track,three-fold stereoscopic and multispectral imagery ofthe earth surface. The MOMS-02rD2 experimentwas the first use of a three-line camera in space.

0924-2716r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0924-2716 99 00034-9

( )H. Ebner et al.r ISPRS Journal of Photogrammetry & Remote Sensing 54 1999 332–341 333

Although the results of this experiment are remark-able, the high accuracy potential of the MOMS-02sensor could not be exhausted due to several prob-lems. These problems, however, have been an impor-tant experience in the preparation phase of theMOMS-2PrPRIRODA mission from the Russianspace station MIR, launched in April 1996.

The photogrammetric processing of the MOMS-02rD2 and MOMS-2PrPRIRODA data is con-ducted by several German university institutes andthe DLR. The major aim is to realize the entirephotogrammetric processing chain, which starts withradiometrically corrected image data and ends up

Ž .with digital terrain models DTM , orthoimage mapsŽ .and vector data for geo-information-systems GIS .

Within the science team the Chair for Photogramme-try and Remote Sensing of the TUM is responsiblefor the reconstruction of the exterior orientation bycombined adjustment and the semi-automatic extrac-tion of linear objects for updating the German GISATKIS-DLM25.

After a description of the two camera experimentsMOMS-02rD2 and MOMS-2PrPRIRODA and thecombined bundle adjustment concept, the results ofthe adjustment using MOMS-02rD2 imagery of or-bit a75b are presented and assessed. Then the resultsof computer simulations on MOMS-2PrPRIRODAimage orientation are discussed. Finally the experi-ences are summarized and an outlook is given.

2. MOMS-02rrrrrD2 and MOMS-2PrrrrrPRIRODAcamera experiments

2.1. MOMS-02rD2 experiment

The optical system of MOMS-02 consists of aŽ .stereo module and a multispectral module Fig. 1 . In

seven different imaging modes certain combinationsof the panchromatic stereo and the multispectralchannels can be selected. The three lenses of the

Žstereo module with 1 CCD sensor array Fairchild.191 each provide three-fold along track stereo scan-

ning with different ground resolutions. The nadirŽ .looking CCD array 4.5 m ground pixel size com-

prises two arrays with 6000 sensor elements each,which are optically combined to one array with 9000sensor elements. The other CCD arrays of the stereo

Fig. 1. Optical system of the MOMS-02 camera. The two inclinedŽ ."21.98 stereo lenses are depicted in the background. In theforeground, the high resolution lens is visible, arranged betweentwo lenses for multispectral data recording.

Žmodule consist of 6000 sensor elements 13.5 m.ground pixel size . In stereo imaging mode 1 8304

sensor elements of the HR channel and 2976 sensorelements of the stereo channels are active.

In the course of the 10 day lasting D2 mission, 48data takes with a data volume of 300 GB wererecorded during 4.5 h, covering an area of about 7Mio. km2. Due to the orbital inclination of 28.58

industrial countries in Europe and North Americahave not been imaged. More detailed informationabout the MOMS-02rD2 camera experiment is given

Ž .by Ackermann et al. 1989 , Seige and MeissnerŽ . Ž .1993 and Fritsch 1995 .

To demonstrate the combined adjustment of im-age, orbit and attitude data, one imaging sequenceŽ . 2mode 1 with 32 120 rows covering 37=430 km

Ž .in Northern Australia orbita75b has been chosenŽ .see Section 4 .

2.2. MOMS-2PrPRIRODA experiment

The MOMS-2P camera is part of the PRIRODAmodule, which is equipped with several remote sens-ing instruments. Overall goals of the PRIRODAŽ .Russ. nature project are to investigate nature pro-cesses and to further develop remote sensing meth-

Ž .ods Armand and Tishchenko, 1995 .The main parameters of the MOMS-

2PrPRIRODA experiment are listed in Table 1. Incontrast to the D2 mission, the MIR orbital inclina-tion of 51.68 also allows for imaging of industrial

( )H. Ebner et al.r ISPRS Journal of Photogrammetry & Remote Sensing 54 1999 332–341334

Table 1Main parameters of MOMS-02rD2 and MOMS-2PrPRIRODA

MOMS-02rD2 MOMS-2PrPRIRODA

Camera carrier Space shuttle MIR space stationMission duration 10 days at least 18 monthsData storage HDT recorder onboard mass memory and

telemetry to ground stationsw xOrbital height km 296 400

w xOrbital inclination 8 28.5 51.6w xGround pixel size nadirrstereo m 4.5r13.5 6.0r18.0

w xSwath width nadirrstereo km 37r78 50r105Geometric camera calibration laboratory laboratory, inflightOrbit information TDRSS tracking GPSAttitude information IMU IMU, star sensor

countries in Europe and North America. Due toseveral problems, only a few MOMS-2PrPRIRODAimages were acquired between September 1996 andApril 1997. Since January 1998 MOMS-2P is operat-ing again.

The camera geometry including the alignment ofthe MOMS-2P camera axes has been determined notonly by calibration in the laboratory, but also by

Ž .inflight calibration Kornus and Lehner, 1997 .A special navigation package MOMSNAV con-

sisting of high precision GPS and Inertial Measure-Ž .ment Unit IMU ensures precise orbit and attitude

data, synchronized with the MOMS-2PrPRIRODAimagery to 0.1 ms. Based on GPS observationsduring a time interval of ca. 5 min and a sophisti-cated short arc modelling, the MIR orbit has beendetermined with 5 m absolute accuracy. The Astro 1star sensor, which is mounted on the QUANT mod-ule of the MIR station provides 10Y. attitude accu-racy. The alignment, however, between the QUANTand the PRIRODA module is known only in theorder of 200Y.

3. Combined bundle adjustment

The photogrammetric point determination is basedon the principle of bundle adjustment and comprisesthe determination of object points and the reconstruc-tion of the exterior orientation of the three-line im-ages. It represents a central task within the pho-

togrammetric processing chain on which all subse-quent products are based.

The collinearity equations

c ˆusu x , x t ,u t 1Ž . Ž . Ž .ˆ ˆŽ .formulate the relationship between the observed im-

Ž .Tage coordinates us u ,u , the unknown objectx yˆ ˆ ˆ TŽ .point coordinates xs X,Y,Z of a point P and theˆ

unknown parameters of exterior orientation x c sˆˆc ˆ c ˆc T ˆ TŽ . Ž .X ,Y ,Z and us v,w,k , respectively, of theˆ ˆ ˆ

image I taken at time t. The orientation angles v, wj

and k have to be chosen in such a way that singular-ities are avoided. In space photogrammetry the threeEuler angles z , h and u , which are related to thespacecraft motion along the trajectory, are well suitedin conjunction with a geocentric object coordinatesystem.

3.1. Orientation point approach

In general, the mathematical model for the recon-struction of the exterior orientation should use sixunknown parameters for each three-line image I . Inj

practice, however, there is not enough information todetermine such a large number of unknowns. In theorientation point approach, the exterior orientationparameters are estimated only for so-called orienta-tion points or orientation images I , which are intro-k

duced at certain time intervals, e.g., once for every1000th readout cycle. In between, the parameters ofeach three-line image I are expressed as polynomialj


functions of the parameters at the neighboring orien-Ž .tation points Ebner et al., 1994 . While this ap-

proach reduces the number of unknown exteriororientation parameters to a reasonable amount, itsinherent disadvantage is that the estimated positionparameters are not associated with a physical modelof the spacecraft trajectory.

3.2. Orbital constraints approach

To overcome this drawback, the bundle adjust-ment algorithm is supplemented by a rigorous dy-namical modeling of the spacecraft motion to takeorbital constraints into account. The camera position

cŽ .parameters x t which have been estimated so farât certain time intervals, are now expressed by thesix parameters of the epoch state vector y andˆ0

additional force model parameters p:ˆ

x c t sx c t , y , p 2Ž . Ž .ˆ ˆ ˆ ˆŽ .0

The force model parameters p may comprise,e.g., the drag coefficient. For the epoch state vectorobservation equations

y sy y 3Ž .Ž .ˆ0 0 0

are introduced, where the observations y are taken0

from the results of the previous orbit determination.Fig. 2 demonstrates the orbital constraints ap-

proach, which exploits the fact that the spacecraftproceeds along an orbit trajectory and all camerapositions lie on this trajectory.

Fig. 2. Orbital constraint approach for the reconstruction of theŽ .exterior orientation of three-line images Ohlhof et al., 1994 .

Compared to the orientation point approach theorbital constraints approach has essential advantages,which can be summarized as follows:Ø Full utilization of the information content of the

tracking data in a statistically consistent way.Ø A reduced number of unknown parameters.Ø Accuracy improvements for the photogrammetric

results as well as the epoch state vector.Statistically, the resulting estimation procedure is

equivalent to a combined orbit determination andbundle adjustment from tracking data and three-lineimage data.

Due to the lack of a dynamical model describingthe camera’s attitude behavior during an imagingsequence, it is not possible to introduce attitudeconstraints into the bundle adjustment in a similarway as the orbital constraints. To this end, theconcept of orientation points is maintained for thecamera’s attitude. The attitude

ˆ ˆ û t su t ,Q 4Ž . Ž .Ž .

of the camera can be represented by the attitudevector Q at selected orientation points. Based on

Ž . Ž . Ž .Eqs. 1 , 2 and 4 , the image coordinates mayfinally be written as

c ˆ ûsu x , x t ,u t su t , x , y , p ,Q 5Ž . Ž . Ž .ˆ ˆ ˆ ˆ ˆŽ . Ž .0

For the incorporation of preprocessed attitude datacorresponding observation equations are formulated.Systematic errors of the attitude observations aremodeled through additional estimation parameters.By limitation to constant and time-dependent linearterms which describe the main effects, six additionalparameters, namely a bias and a drift parameter foreach attitude angle, are used for each orbital arcŽ .s imaging sequence .

The observation equations for the attitude parame-ters, which are introduced at selected orientationpoints, are given by

ˆ ˆQsQ Q ,b , 6Ž .Ž .ˆwhere b denotes the unknown bias and drift parame-

ters.The mathematical model of the orbital constraints

Ž .approach is described in detail in Ohlhof 1996 andŽ .Ohlhof et al. 1994 .


4. Practical results of MOMS-02rrrrrD2 image ori-entation

This section describes the orientation of MOMS-02rD2 imagery based on the orientation point ap-proach. Four image scenes a15 to a18 of the D2

Ž .orbit a75b nomenclature of DARA, 1994 wereselected, covering an approximately 37=430 kmwide area in Northern Australia. Besides several tiepoints, calibration data, navigation data and 64ground control and check points are considered asadditional information in a combined adjustment.

During the last 2 years the Australian MOMS-02rD2 data set was also evaluated by other research

Ž .groups in Zurich Baltsavias and Stallmann, 1996 ,Ž . ŽMelbourne Fraser and Shao, 1996 , Munich Dorrer.et al., 1995 and Glasgow. The four groups used

different input data sets and different mathematicalmodels. Most of the point determination results,however, fit in quite well with the results describedin this paper.

4.1. Input data

The image coordinates of tie points were derivedautomatically by a modified region-growing match-

Ž .ing algorithm Otto and Chau, 1989 , which wasŽapplied successfully in the past to SPOT Heipke and

. ŽKornus, 1991 and airborne MEOSS imagery Heipke.et al., 1996 . From this information a sparse and a

dense subset of regularly distributed points wereselected to be fed into the adjustment. According toexperiences of the former evaluations, a standarddeviation of 0.3 pixel for the image coordinates wasassumed.

The calibration data were provided by the Ger-Ž .man aerospace company DASA former MBB , the

Ž .manufacturer of MOMS-02 DASA, 1994 . Correc-tion tables describe deviations of certain CCD pixelsŽ .500 pixel distance from their nominal positions inthe image plane. The functional model of the interiororientation employs 9 parameters per lens or per

Ž .channel, as described in Ebner et al., 1994 . A 10thparameter, modelling a second order sensor curva-ture, was added, since band-to-band registration ofthe first MOMS-2PrPRIRODA imagery yielded sys-tematic non-linear deviations from the calibration

Ž .data of the multispectral channels Kornus, 1996 . In

order to compensate for possible deviations of thestereo channels, the lab-calibrated parameters of theinterior orientation were introduced with low weightinto the adjustment allowing for the simultaneousestimation of deviations, at least to some extent.

The naÕigation data were provided by NASA andŽ .processed by Geo-Forschungs-Zentrum GFZ Pots-

dam. The orbit positions were compiled from TDRSSDoppler measurements, which were fed as observa-tions into the orbit determination software of GFZ

Ž .Potsdam Braun and Reigber, 1994 , yielding a rela-tive orbit accuracy of 3 m and an absolute accuracy

Ž . Ž . Ž .of 14 m radial , 32 m lateral and 31 m tangential .The gyro data were already preprocessed by NASAand provided as a time series of Euler angles at 1 stime interval with a relative accuracy of 20Y. Sincethe alignment between the MOMS camera axes andthe gyro axes was not calibrated, there is no absolutepointing knowledge. Both Euler angles and orbitpositions were transformed into a local topocentriccoordinate system with fundamental point at fs21830XS, ls136800X W, hs300.0 m. Based on ap-proximation tests 8 orientation points were selected,having a distance of 4612 rows between each other.

( )Seventy-seven ground control points GCP weremeasured by Melbourne University using differential

Ž .GPS Fraser et al., 1996 . The points are located in a37=100 km wide flat desert area covered by imagescene a17. Most of the targets represent road junc-tions or dams of artificial water basins, which couldbe identified in the imagery with about 1 pixelprecision. At ETH Zurich 68 GCP were measured in

Ž .the channel ST6 imagery forward and automati-Ž .cally transferred to channel ST7 aft . At DLR 49 of

Ž .these points were transferred to channel HR5 nadirfrom both ST6 and ST7 imagery. From the differ-ences in HR5 a standard deviation of 0.4 pixel forthe GCP image coordinates was derived. For theGCP object coordinates ss1 m was chosen in

Ž .height and ss13.5 m 1 pixel in planimetry, dueto the identification uncertainties.

4.2. Results

First adjustment runs using 4 GCP yielded incon-sistencies in the input data: An 11.4 km bias of theorbit positions in flight direction was interpreted as atime mismatch between position data and image line


Fig. 3. Configuration of control and check points.

recordings in the order of 1.6 s. Further adjustmentruns using all GCP led to the rejection of 4 GCP dueto large planimetric residuals. From the remaining 64

Ž .GCP root-mean-square rms residuals of 9 m in X,8 m in Y and 0.1 m in Z were obtained. The Zcomponent is quite small due to the high weighting

Ž .of the GCP Z coordinates ss1 m compared to theweighting of the corresponding image coordinatesŽ .ss0.4 pixel . The planimetric residuals of nearly10 m reflect the identification uncertainty mentionedabove.

In a series of adjustment runs using subsets of 4,10 and 20 GCP, empirical accuracies were derivedfrom the remaining 44 points, which served as inde-

Ž .pendent check points see Fig. 3 .The Tables 2 and 3 contain the empirical accura-Ž .cies rms values computed for the different GCP

configurations and sets of tie points using all naviga-Ž . Ž .tion data Table 2 and orbit data only Table 3 .

The comparison between Tables 2 and 3 shows nosignificant differences in the results, indicating thatattitude information is not required. From Tables 2and 3 it can be seen that the results are only slightlyimproved if 1000 instead of 100 tie points are used.Despite of the given uncertainties, a height accuracyof up to 4.1 m is obtained, corresponding to 0.3 ofthe ground pixel size of the oblique looking channels

Table 2Ž .Empirical accuracies rms values ´ using all navigation data

1000 tie points 100 tie points

4 GCP 10 GCP 20 GCP 4 GCP 10 GCP 20 GCP

w x´ m 11.6 10.8 10.3 11.6 11.0 10.1Xw x´ m 12.8 9.3 8.9 12.8 9.7 9.4Yw x´ m 4.1 4.6 4.3 5.3 4.9 4.7Z

Table 3Ž .Empirical accuracies rms values ´ using orbit data only

1000 tie points 100 tie points

4 GCP 10 GCP 20 GCP 4 GCP 10 GCP 20 GCP

w x´ m 10.8 10.5 10.0 11.4 10.6 9.5Xw x´ m 12.6 9.8 9.3 13.9 10.0 9.4Yw x´ m 4.1 4.5 4.3 5.2 4.6 4.6Z

Ž .13.5 m . The planimetric accuracy potential ofMOMS-02rD2 is not verified, since the GCP andcheck points could not be identified in the imagerywith the required accuracy.

5. Computer simulations on MOMS-2P rrrrrPRIRODA image orientation

A series of computer simulations have been car-ried out to analyze the effect of certain parameterson the accuracy of MOMS-2P image orientation,especially the effect of block configuration and con-trol information.

5.1. Input parameters

5.1.1. Block configurationsThe computer simulations were performed for

three different block configurations:Ø Single stripØ Block of six strips with qs20% side overlapq

two crossing stripsØ Block of 13 strips with qs60%q two crossing

Ž .strips Fig. 4

Fig. 4. Block consisting of 13 strips with four baselengths eachand 60% side overlapqtwo crossing strips. The region of interestis within the dotted lines. The GCP locations are marked with atriangle.


The strip length was chosen to four baselengthsŽ .640 km . This results in the fact that points at thebeginning and the end of the single strip are pro-jected into two images only, whereas each point inthe central part of the strip is projected into threeimages. The strip width amounts to 50 km. The

2 Žentire block covers 320=250 km without two-ray. Žarea , corresponding to the area of Catalonia 270=

2 .250 km , which was thought to be the most impor-tant test site of the MOMS-2P experiment.

5.1.2. Interior orientation parametersAll parameters of the interior orientation were

introduced as error-free values.

5.1.3. Conjugate pointsThe object coordinate system is defined as

topocentric Cartesian system XYZ with the positivedirection of the X-axis parallel to the direction offlight. The object points are arranged in two differentgrids:

Case 1: D Xs40.0 km, DYs20.0 km, Zs0.0 km.

Case 2: D Xs2.0 km, DYs10.0 km, Zs0.0 km.

Consequently the single strip consists of 27 andthe blocks contain 117 object points in the first case,whereas the single strip consists of 805 and theblocks contain 4025 object points in the second case.For each block configuration, the image coordinatesof the object points were computed assuming a flightpath with a constant altitude of 400 km and attitudevalues equal to zero.

In case 1 only a few conjugate points are includedŽ .which can be measured high precisely ss0.1 pixel

using a digital stereo comparator, whereas in case 2additional tie points derived from digital image

Ž .matching ss0.3 pixel are introduced. Thus, wehave the following two cases for the image coordi-nates, which were treated as being uncorrelated:

Case 1: ss0.1 pixel for all image coordinates.

Case 2: ss0.3 pixel for all image coordinates,Ž . Ž .except for the 27 points strip and 117 points block

of Case 1, respectively, having ss0.1 pixel.

5.1.4. Ground control informationThe simulations have been carried out for two

different configurations of ground control informa-tion:

Case a: no ground control.

Case b: 16 GCP with s ss ss s1.0 m.X Y Z

The 16 GCP are arranged in four groups of fourpoints each, located at the corners of the at leastthree-ray area of the strip or the block. The standarddeviations of the GCP’s image coordinates are as-sumed to 0.3 pixel.

5.1.5. Orbit and attitude obserÕationsFor the orbit and attitude observations two differ-

ent cases were investigated:

Ž .Case A: error-free observations ss0 .

Case B: realistic orbit and attitude observations.Ž .Table 4

Case A defines the accuracy limit, whereas case Bis the realistic one. In Table 4 the standard deviationsdescribing the relative accuracy of the position pa-rameters are nearly zero, since all camera positionsare constrained to lie on the orbit trajectory. Thestandard deviations describing the absolute accuracyare 5 m for the position and 2 cmrs for the velocitycomponents of the epoch state vector. For eachorientation point attitude observations were intro-duced with a relative accuracy of 10Y. Due to thepoor alignment precision of the MOMS-2P camerawith respect to the Astro 1 star sensor, no observa-

Table 4Standard deviations of the observed position and attitude parame-

Ž .ters –: no observation

Position AttitudeYRelative 0.1 m 10

Absolute position 5.0 m –velocity 2 cmrs –

Absolute bias – –Ydrift – 0.16 rs


tions for the attitude bias are assumed. The drift ofthe IMU gyros should not exceed 0.16Yrs during oneMOMS-2P imaging sequence.

Based on experiences with MOMS-02rD2 data,the distance between the orientation points was cho-

Ž .sen to 4940 rows ca. 90 km leading to nine orienta-tion points per strip.

5.2. Results

Ž .For analysis, the rms values m planimetryˆ ˆX YŽ .and m height of the theoretical standard deviationsZ

s , s and s of all points within the dotted linesˆ ˆ ˆX Y Z

in Fig. 4 were calculated. Moreover, the rms valuesm of the theoretical standard deviations of theˆ ˆzhuˆ

ˆ ˆestimated exterior orientation parameters z , h, u atˆthe orientation points were computed. All accuracyfigures were derived from the inverted normal equa-tion matrix. In case of a free adjustment the sevendata parameters are determined by minimizing thetrace of the covariance matrix of the estimated objectpoint coordinates. So the free adjustment representsthe interior accuracy of point determination. In Figs.5–8 the rms values m and m are shown graphi-ˆ ˆ ˆX Y Z

cally.First the results of the single strip and block

Ž .adjustments with GCP are discussed Figs. 5 and 6 .Ž .Assuming error-free position and attitude data A ,

the accuracy of point determination only depends on

Fig. 5. Rms values m for different block configurations withˆ ˆX YŽ . ŽGCP case b , observed position and attitude parameters cases A. Ž .and B and different number of object points cases 1 and 2 .

Fig. 6. Rms values m for different block configurations withZŽ . ŽGCP case b , observed position and attitude parameters cases A. Ž .and B and different number of object points cases 1 and 2 .

the standard deviations of the image coordinates, thenumber of tie points and the geometric constellationof the ray intersections. The rms values are 1.1 m inplanimetry and 3.5 m in height for the single strip.The planimetric and height accuracies decrease onlymoderatly, if the position and attitude data are intro-

Ž .duced with realistic standard deviations case B ,Ž .even with a small number of tie points case 2 .

Using the equal number of GCP the accuraciesimprove by factor 1.4 for the qs20% blocks and by

Fig. 7. Rms values m for different block configurations withoutˆ ˆX YŽ .ground control case a , observed position and attitude parameters

Ž . Žcases A and B and different number of object points cases 1.and 2 .


Fig. 8. Rms values m for different block configurations withoutZŽ .ground control case a , observed position and attitude parameters

Ž . Žcases A and B and different number of object points cases 1.and 2 .

factor 1.8 for the qs60% blocks compared to thesingle strip, due to the increasing block strength. Theblocks with qs60% and two additional crossingstrips provide excellent rms values of about m sˆ ˆX Y

0.9 m, m s2.5 m and m s1.6Y, respectively, inˆ ˆ ˆZ zhuˆcase 2.

From Figs. 5 and 6 it can be also seen that thenumber of tie points has only little influence on therms values for the blocks. Even a small number of117 points provides high accuracies in planimetryand in height.

In the following the adjustment results withoutŽ .GCP are analyzed Figs. 7 and 8 . The single strip

leads to an undetermined configuration because noobservations are available for attitude bias, and otherobservations are not able to compensate for that. If ablock with qs20% and two crossing strips is ad-justed, all angles are determined due to the absoluteposition data, which were introduced for each stripof the block. A comparison of Figs. 7 and 8 withFigs. 5 and 6 shows that the object points are lessaccurate, if no GCP are introduced at all. A high

Ž .number of conjugate points case 2 , however, leadsto improvements of factor 1.3 for m and mˆ ˆ ˆX Y Z

Ž .compared to a small number of points case 1 . Thebest accuracies without ground control are achievedusing observed position and attitude parameters forblocks with 13q2 strips and 4025 tie points, where

the rms values amount to m s3.5 m, m s4.6 mˆ ˆ ˆX Y Z

and m s2.3Y, respectively.ˆ ˆzhuˆ

6. Summary and outlook

The reconstruction of the image orientation of theMOMS-02 camera is based on a combined adjust-ment of the complete image, ground control, orbitand attitude information. The combined adjustmentmakes use of the orientation point approach or theorbital constraints approach. In the second case, thebundle adjustment algorithm is supplemented by arigorous dynamical modeling of the spacecraft mo-tion.

The results of the combined adjustment usingMOMS-02rD2 imagery and control information oforbit a75b are presented. Based on the orientationpoint approach an empirical height accuracy of up to

Ž .4 m 0.3 pixel is obtained. In planimetry the empiri-Ž .cal accuracy is limited to about 10 m 0.7 pixel ,

since the GCP and check points could not be identi-fied in the imagery with the required accuracy.

Computer simulations on MOMS-2PrPRIRODAimage orientation based on realistic input informa-tion have shown that good accuracies of the esti-mated exterior orientation parameters and object pointcoordinates can be obtained either with a single stripand a few precise GCP or even without groundcontrol information, if a block of several overlappingand crossing strips with high geometric strengthŽ .qf60% is adjusted.

In near future the evaluation of real MOMS-2PrPRIRODA data will show whether the modelsand findings of the simulations can be confirmed.First results based on nine image scenes of orbitT083C covering parts of Southern Germany and

Ž .Austria have been presented by Kornus et al. 1998 .

Acknowledgements

The help of H. Froba, who performed most of the¨MOMS-2PrPRIRODA simulation runs, is gratefullyacknowledged. The work presented in this paper isfunded by grants 50 QS 9008 and 50 QM 9205 of

Ž .the former German Space Agency DARA .


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