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Model Development and Testing for Themis Controlled Mars Mosaics Lunar and Planetary Science XXXVI (2005) 2052.pdf MODEL DEVELOPMENT AND TESTING FOR THEMIS CONTROLLED MARS MOSAICS. B. A. Ar- chinal1, S. Sides1, L. Weller1, G. Cushing1, T. Titus1, R. L. Kirk1, L. A. Soderblom1, and T. C. Duxbury2, 1U. S. Geological Survey (2255 N. Gemini Drive, Flagstaff, AZ 86001, USA, [email protected]), 2Jet Propulsion Labo- ratory (4800 Oak Grove Drive, M/S: 264-379, Pasadena, CA 91109, USA, [email protected]). Introduction: As part of our work [1] to develop tech- orientation while the line scanner image is being collected, niques and procedures to create regional and eventually thus [4, pp. 290-291]: global THEMIS mosaics of Mars, we are developing algo- ⎡ 2⎤ X 0 + X1(t − tR ) + X 2 (t −t ) rithms and software to photogrammetrically control ⎡X s ⎤ ⎢ R ⎥ ⎢ ⎥ 2 , THEMIS IR line scanner camera images. We have found Y = ⎢ Y + Y (t − t ) + Y (t −t ) ⎥ from comparison of a limited number of images to MOLA ⎢ s ⎥ ⎢ 0 1 R 2 R ⎥ ⎢Z ⎥ 2 digital image models (DIMs) [2] that the a priori geometry ⎣ s ⎦ ⎢ Z + Z (t − t ) + Z (t −t ) ⎥ ⎢ 0 1 R 2 R ⎥ information (i.e. SPICE [3]) for THEMIS images generally ⎣ ⎦ allows their relative positions to be specified at the several ⎡ 2⎤ αˆ +αˆ (t − t ) +αˆ (t −t ) pixel level (e.g. ~5 to 13 pixels). However a need for con- ⎡αˆ⎤ ⎢ 0 1 R 2 R ⎥ 2 , trolled solutions to improve this geometry to the sub-pixel ⎢ ˆ⎥ ⎢ ˆ ˆ ˆ ⎥ δ = δ0 + δ1(t − tR ) + δ 2 (t −t ) level still exists. Only with such solutions can seamless ⎢ ⎥ ⎢ R ⎥ ⎢κ ⎥ 2 mosaics be obtained and likely distortion from spacecraft ⎣ ⎦ ⎢κ + κ (t − t ) + κ (t −t ) ⎥ ⎣⎢ 0 1 R 2 R ⎦⎥ motion during image collection removed at such levels. Past experience has shown clearly that such mosaics are in heavy where X0, Y0, and Z0 is the position of the spacecraft at some demand by users for operational and scientific use, and that reference time tR, e.g. the time of the central line of a particu- they are needed over large areas or globally (as opposed to lar image. Similarly, the camera orientation at that moment being available only on a limited basis via labor intensive is given by the J2000.0 right ascension and declina- custom mapping projects). Uses include spacecraft naviga- ˆ ˆ tionαˆ0 ,δ 0 , and twist angleκ0 . Xs, Ys, Zs,αˆ , δ , and tion, landing site planning and mapping, registration of mul- tiple data types and image sets, registration of multispectral κ are the corresponding values at the time t of any line in images, registration of images with topographic information, the image. To allow for unknown variations in the space- recovery of thermal properties, change detection searches, craft position and orientation while the image is being ob- etc. tained, we will solve for some or all of the additional un- knowns shown. Algorithms for Adjustment of THEMIS IR images: Procedures for the photogrammetric adjustment of standard Of course, with such a technique there are still a number framing camera (e.g. using film or electronic detectors such of additional issues that must be addressed. For example, as vidicons or areal CCDs) have been well developed, ini- this procedure could result in up to 9 additional parameters tially for terrestrial photogrammetry [4], but also since the for positions (3 in position, velocity, and acceleration) and 6 1970’s for planetary photogrammetry [5]. Attempts at pho- in orientation (3 in both velocity and acceleration, in addition togrammetric adjustments using line-scanner camera images to the 3 orientation angles) per image. If an image is in some however are fairly recent, having first been developed for way collected discontinuously – e.g. due to data dropouts or terrestrial aerial and orbital uses in the 1980’s and ‘90’s [6], sudden spacecraft motion – additional sets of parameters will and for limited mapping with Mars Orbiter Camera (MOC) also need to be determined for each image segment. To narrow angle images in the last few years [7]. However, solve for such additional parameters, additional tie points general procedures for handling such images and particularly will indeed be needed between overlapping images. THEMIS IR images have not yet been developed and are Additional effort will also be needed to estimate the a now the focus of our work. priori values of the polynomial parameters, based on the Our adjustment procedure is based primarily on an ex- initial estimates of exterior orientation (derived from the tension of the techniques and software used for the adjust- input SPICE data). ment of framing camera image measurements, e.g. those The polynomial parameters will also likely be highly developed at RAND and currently used at USGS [8]. The correlated. In fact, in our past planetary mapping photo- fundamental difference with line scanner images vs. framing grammetric solutions [5, 8], spacecraft position has always camera images is that the camera position and orientation been held fixed and never been solved for along with space- must be determined at the exposure of every line, rather than craft orientation, since for the relatively narrow angle cam- more simply at the exposure of every image. Obviously a eras in use, these parameters are highly correlated. It will be direct extension of solving independently for such informa- necessary to address these correlations – so that a solution tion (exterior orientation) at every line of a line scanner cam- can be achieved – by weighting the polynomial parameters era, even assuming a much larger number of image tie point based on realistic accuracy estimates for the a priori exterior measurements were available, would result in an underde- orientation information (e.g. orbit position and camera point- termined system of equations. As has been done in terres- ing accuracy). We will also experiment with various image trial mapping [6] we therefore propose to reduce the number sets in order to determine the usefulness of solving for the of parameters required for a solution to a reasonable level, higher order parameters, e.g. spacecraft acceleration and by solving for simple polynomial expressions for the exterior orientation acceleration. It is likely that for many solutions, e.g. with images that do not cover substantial arcs along the Lunar and Planetary Science XXXVI (2005) 2052.pdf planetary surface, the full parameterization will not be any given pair of images. Different matching algorithms needed in order to obtain sub-pixel accuracy. might be used, e.g. for different instruments, area matching, Current testing. We are currently completing the man- point of interest matching, texture matching, feature match- ual measurement of tie points (using ISIS qmatch) [9] for a ing (craters), etc. A third part will be the automatic rejection number of THEMIS IR images covering the two MER land- of outliers to the photogrammetric adjustment software, in ing site ellipses. We also plan to work on one additional area order to minimize or even eliminate manual checking of tie (such as any prime Phoenix landing site ellipse). We are point measurements. making a dense set of tie point measurements between a few In large photogrammetric solutions (e.g. with tens of pairs of images in order to ascertain the best initial set of thousands or more of measures, images, and parameters) the parameters, weights to be used and numbers of tie points method of conjugate gradients [10] can be used to complete needed for image pairs. Tie points are also being measured solutions. However a better solution method would be true between the THEMIS images and MOLA DIMs in order to block adjustment solutions, i.e. solutions where image cov- provide absolute control for the images (at least at the ~100 erage is broken into regions and correlations between regions m (~1 THEMIS IR pixel) accuracy of the MOLA data [2]. (except for image overlap between regions) are ignored. Once photogrammetric solutions are successfully completed, This would reduce the solution round-off error, and allow for we will use the updated exterior orientation information nested (blocked) matrix inversion solutions. The latter could (updated SPICE) in ISIS to generate controlled mosaics of provide any desired parameter uncertainties, and possibly these areas, both to assist in the final evaluation of our tech- provide for faster solutions (vs. conjugate gradient solu- niques and as useful products for use in the study of these tions). sites. So scaling up solutions from using a few images to re- Future development. An immediate goal of this work gional or global datasets is still an area that needs thus, to be will be to demonstrate the control of THEMIS IR to addressed. However, the basic adjustment procedures (de- THEMIS VIS images by adjustment of a limited set of VIS scribed here) and the likely necessary block adjustment tech- images to the IR mosaics. This will assist in the evaluation niques are tractable. Beyond this, the significant issues that of such a line scanner to framing camera image adjustment will require future attention are developing reliable auto- technique and also provide absolutely controlled VIS mosa- matic tie pointing procedures – to provide the measurement ics of these areas. Later we also hope to demonstrate the use input to the solutions – and to handle the sheer volume of of this technique to adjust other types of images and combi- images and measurements involved. nations of images, such as THEMIS IR band to band, Summary: We are in the process of developing the al- THEMIS IR to other framing camera images (e.g. Viking), gorithms and software to make controlled mosaics of Mars Express HSRC images, Mars Reconnaissance orbiter THEMIS IR images.
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