Phobos Shadows

Glen W. Deen

May 3, 2002

Introduction

To be honest, I was looking for a “smoking gun”, and I didn’t find one.  Because a particular theory required that Phobos be ejected from Mars in early June of 2000, I had hoped to find Phobos shadows on Mars up to some date and none afterward, and that would tend to support the theory.  I did find that Phobos shadows were missing after September 20, 2000, but I also found that the reason was that after that date the equator of Mars, and therefore the orbit of Phobos, was tilted so much with respect to the orbit of Mars that the shadow of Phobos had moved beneath the South Pole of Mars and was projecting into empty space.  Furthermore, the theory in question required a much earlier ejection.  September 20, 2000 was more than three months too late.

I have previously speculated in 76P Collision Theory and The Phobos Mystery Continues that Phobos may have been ejected from its orbit around Mars as a result of a close encounter with Comet 76P/West/Kohoutek/Ikemura in June 2000.  That did not happen, and so those speculations are wrong.  Nevertheless, I found that 56 consecutive mapping swaths (among 121 consecutive images) are either missing or censored from June 5 to June 9, 2000, and this begs the question as to whether the camera might have been aimed at Comet 76P instead of the surface of Mars.

I was also wrong about Deimos when I published Phobos and Deimos Have Vanished.  I sincerely regret that mistake, and I apologize to all of my readers for having made it.  Ironically, when I published that mistaken article on August 21, 2000, I had already looked at the photograph that I had taken two days earlier that contained the image of Deimos, but I did not see it at that time.  It was not until weeks later that I looked at the same photograph again, and I saw it.  This photograph is shown in Glen Deen Captures Martian Satellite.  Deimos is the small white spot in the glare of Mars just to the left of the arrow.

This current article about Phobos Shadows does not rule out the possibility that Comet 76P may have experienced an orbit deflection as a result a close encounter (or a collision) with Mars and that the same comet (or ejected debris from an impact) may impact Earth as speculated in Possible Comet impact in Iraq on June 10, 2002, nor does it rule out the possibility that Phobos may have been ejected by the event that initiated the Martian global dust storm on July 2, 2001.  It only rules out the involvement of Phobos in the imputed June 2000 encounter of Comet 76P with Mars, if such an encounter occurred.

As a result of my present study of its eclipse shadows in the Mars Global Surveyor (MGS) Mars Orbital Camera (MOC) wide-angle mapping swaths, I can say unequivocally that Phobos was still in its regular orbit as recently as September 20, 2000.  At that time, its shadow was very near the South Pole and heading south into space.  It should have returned to the Martian South Polar region around March 6, 2001 heading north, but no mapping swaths have been published after January 31, 2001.  The only way I could be wrong about this would be if Malin Space Science Systems (MSSS) added shadows to images that had no shadows, and I do not believe they did that.  Because if they did add missing shadows, they would not have added any extra mysterious shadows, thereby raising questions.

Two Shadows Twice

There are at least two mysteries to be solved.  The mapping swath for the September 13, 2000 orbit 6788 shows two shadows!  (See Orbit 6788 – Two Shadows below.)  The most reasonable explanation that I can think of is that Phobos had a visitor in the form of another space body.  If so, this visitor was not near enough to affect the orbit of Phobos because Phobos experienced its last recorded solar eclipse 7 days later in orbit 6870 on September 20, right on schedule.  The only alternative explanation for the extra shadow is that it is a transient surface feature such as a dust or a smoke plume.  (But plumes ought not to be almond-shaped.)  The second mystery is that Orbit 6706 on September 6, 2000 (7 days earlier) also shows two shadows, and the extra shadow in this picture is very long, straight, and striated.  The most reasonable explanation for this elongated shadow (if it is not a flat disk-shaped object that is tumbling in a retrograde solar orbit) is that it is a smoky bolide trail.  The only alternative explanation for this extra shadow is, once again, a transient surface feature.  Pictures of it are shown below at Orbit 6706 Also Has Two Shadows.

Finding the Phobos Shadow Images in the MGS Mapping Swaths

I could not have found the shadows of Phobos (nor would I have even thought to look for them) if it were not for the NASA article at http://mars3.jpl.nasa.gov/mgs/msss/camera/images/11_1_99_phobos/index.html that showed four Phobos shadows (August 26, September 1, 8, and 25, 1999).  This gave me a starting point, and that was all I needed.   Yesterday (May 2, 2002) I saw that this link is broken again, and it is still broken today.  It was broken in April when I was composing this article, but I found it to be working again as recently as 10 days ago.  Trusting soul that I am, I did not download this web page and its pictures.  If any reader finds this link to be working again, please e-mail me at glen.deen@gte.net so I can download it and then upload it to my website and put a working link to it in this article.

The MGS spacecraft maps the entire surface of Mars again and again with its wide-angle cameras simultaneously with high-resolution strips with its narrow-angle cameras.  It gets overlapping wide-angle swaths of the day lit side of Mars on almost every orbit with each swath containing identical red-filtered and blue-filtered images.  There are gaps where orbit swaths are missing from the published data set.  Some gaps are explained, and others are not explained (see Did Malin Space Science Systems Censor Data?).   The period of the MGS spacecraft’s orbit is 1.96078418 hours.  The sidereal period of Phobos’s orbit is 7.653622327 hours, but eclipses depend on its synodic period (new moon to new moon).  Because Mars’s orbit is not circular (its eccentricity is 0.0933), the synodic period of Phobos varies throughout the Martian year.  The average synodic period over the time span of this data set is 7.6573137 hours, but it ranges from a minimum of 7.6566293 hours to 7.6579138 hours.

If we divide the average synodic period by the MGS period, we get 3.90523 MGS orbits to one Phobos orbit.  This ratio is nearly four, and there are several instances in which eclipses are spaced four MGS orbits apart.  When that happens, one shadow will be near the left-hand edge of the swath, and the other shadow will be near the right-hand edge.

The intervals between observed eclipses with no displacement in longitude would be such that both MGS and Phobos will have experienced an integral number of orbits between eclipses.    We find that the following integral ratios come close to that actual orbit period ratio.

39/10 = 3.90000 = 3.90523 – 0.00523

43/11 = 3.90909 = 3.90523 + 0.00386

82/21 = 3.90476 = 3.90523 – 0.00047

Therefore, we often find sequences of Phobos shadows at intervals of . . . , 39, 43, 39, 43, . . . MGS orbits because we note that 39 + 43 = 82, and 82/21 is a good approximation to the actual orbit ratio.  Therefore, once you discover one Phobos shadow, it is easy to know where to look for the next one.   If you don’t find one 4 orbits later or 39 orbits later or 43 orbits later, you will almost always find one 82 orbits later.  Since 39 + 4 = 43, we find that when an interval of 4 orbits exists between subsequent shadows, the interval sequence is either . . . , 39, 4, 39, . . . or . . . , 39, 4, 82, . . . or . . . , 82, 4, 39.

I found 86 Phobos shadows in this data set.  It is interesting to examine the frequency of each of the possible intervals of 4, 39, 43, and 82 MGS orbits.  I found 3 intervals of 4 orbits, 28 intervals of 39 orbits, 31 intervals of 43 orbits, 20 intervals of 82 orbits, one gap of 1324 orbits, and one gap of 289 orbits.  I explain these gaps below, but even the gaps are related to intervals of 39 and 43 orbits.  1324 = 13 x 39 + 19 x 43 and 289 = 3 x 39 + 4 x 43.  There is a gap of 55 orbits (121 images) from June 5, 2000 through June 9, 2000 that is not explained.  (See Did Malin Space Science Systems Censor Data?.)

Unlike Earth’s Moon, which rarely casts its shadow onto the Earth’s surface because its orbit is so large and it is inclined to Earth’s equator, Phobos nearly always casts its shadow onto the surface of Mars because its orbit is small and it is in Mars’s equatorial plane.  The only exceptions are when its shadow goes north of the North Pole as it did from November 7, 1999 to February 23, 2000 or it goes south of the South Pole as it did from September 13, 2000 to March 3, 2001.  This is best illustrated with a plot of my Phobos shadow findings.

Each symbol in the graph is an observation by the MOC of the shadow of Phobos in one of the wide-angle swaths.  The earliest observation in the chart is orbit 1098 on June 7, 1999 (actually June 06, 1999 at 18:25:45 but the chart rounds up the date).  I started looking on that date because that is the earliest observation where both red-filtered and blue-filtered images are published.  Before that only blue-filtered images are published.  That may be because the spacecraft’s orbit was near the right-hand terminator (viewed from the Sun) on this date and earlier.

The ordinate axis in the graph is the vertical position of the shadow expressed as a percentage of the swath from start (South) to stop (North).  So, 100% is near the North Pole, and 0% is near the South Pole, and that puts North at the top of the chart.  But note that the South Pole is at the top of the raw MOC wide-angle swath images, since the camera scans from the top to the bottom of the image, and the spacecraft orbit goes from South to North in the daylight hemisphere.  That means that surface features in these images are upside down.

The 1324-orbit gap in the shadow image sequences between November 7, 1999 and February 23, 2000 is the result of the shadow of Phobos being north of the North Pole, as I mentioned above.  The 289-orbit gap between June 21, 2000 and July 15, 2000 occurred when Mars was near the Sun as viewed from Earth, and Mars was exactly behind the Sun (in longitude but slightly above it in latitude) at the midway point in that gap.  Evidently, radio noise from the Sun interferes with the radio signal from the spacecraft, and the angle subtended at Earth across this gap corresponds to the beam width of the receiving antenna.

How Are Shadows Confirmed?

A shadow is confirmed when the following criteria are all satisfied: (1) it is present in both the red-filtered and blue-filtered images, (2) it is absent in another swath (at a different time) covering the same latitude and longitude, and (3) it’s position in the swath falls on (or very near) the curve plotted in the above chart.  The curve would have been smoother if I had plotted the latitude of the shadow instead of the position in the image against the orbit number instead of the date, but the conversion did not seem to be worth the effort.

The first criterion rules out clouds and most surface features that look different through red and blue filters.  The second criterion rules out those few surface features that appear similar through red and blue filters.  The third criterion is an independent confirmation imposed by the eclipse ray geometry and the orientation of the equator of Mars relative to its orbit.  This principle of Phobos shadow confirmation is illustrated in the pictures of Orbit 5554 below.  The red-filtered image can be seen at http://ida.wr.usgs.gov/display/MGSC_1106/m16002/m1600263.imq.jpg, and the blue-filtered image can be seen at http://ida.wr.usgs.gov/display/MGSC_1106/m16002/m1600264.imq.jpg.  (These are thumbnail pictures.  Move the mouse pointer to the lower-right-hand corner of the picture to make an expansion button appear, then click that button to see the image displayed full size.)

This is a good example because both the sub-solar point and the shadow of Phobos are near the equator so the eclipse ray is vertical to the surface.  That makes the shadow sharper and more easily seen than when the eclipse ray is not vertical.  (At higher latitudes, near one of the poles, the shadow is larger and more diffuse.)  The bright vertical streak in the images is the reflection of the Sun, and the center of that streak is the sub-solar point.  That is the point at which a ray from the Sun to the center of Mars passes through the surface.  The images above have been cropped to conserve space, and the scale has been magnified, but they are otherwise copies of the MOC mapping swath raw images at the URLs given for them.  The shadow of Phobos is the small dark oval that is slanted in the 2 o’clock direction (+30º from the horizontal) and positioned slightly above and to the right of the sub-solar point.  The elongation and the slant of the image occurs because the camera is scanning downward in time, and the shadow is moving to the left in this upside-down field of view.

The reference orbit number 5466 shows exactly the same surface features (because it has approximately the same central latitude and longitude as orbit 5554), and the shadow is absent.  Therefore what we are calling a shadow is not a surface feature.  The time given in orbit 5466 is halfway between the start and stop times.  The time given in orbit 5554 is the eclipse time, i.e., the time that the shadow appeared in the camera’s field of view, which is 48.9% of the span between the start and stop times.

The Surface Locus of the Shadow of Phobos

The spacecraft was given about as good a Sun-synchronous orbit as you can get with a planet having an eccentric orbit.  The MGS orbit is inclined from a perfectly polar orbit by about 3º so that the period of its orbit precession is about one Martian year.  Within the time frame of this data set, the swaths begin near the right-hand terminator and move towards the left.  The timing of the starting and stopping of each scan is set to correspond with the daylight portion of each orbit.

At no time does the locus of the shadow ever come close to the left-hand terminator in this data set.  This is easily seen in the following nine diagrams of Mars as seen from the Sun and plotted by the Guide 7.0 CD-ROM star-charting program, which is created and distributed by http://www.projectpluto.com/.  The shadow’s vertical position in the swath is expressed in percent of the scan from start to stop, which is approximately the same as the percentage of the semi-circumference from the South Pole going North.  The scan goes between the illuminated edges of the disk, not between the poles.  Because the MGS orbit is canted about 3º from the nearest meridian, whichever pole is illuminated by the Sun is always visible at its end of the scan.  The orbit of Phobos is approximately in the equatorial plane, but it appears either above or below the equator in these solar views according to how much the planet’s equator is tilted with respect to its orbit plane.

The times given in the lower-left corner of each diagram are at the Sun, and they are later than the eclipse times observed by the MGS spacecraft by the light-travel time from Mars to the Sun.  The grid lines in the diagram are drawn at 15º intervals.  When Phobos is near the equator, as viewed from the Sun, the shadow position is roughly 50% of the distance from the South Pole to the North Pole, as you can see in orbits 1836 and 5554.  In orbit 1836, Deimos happens to be quite near Phobos from the Sun’s point of view.  However Deimos does not cast a noticeable shadow because it is too far away from the surface of Mars.  From the surface, Phobos would obscure a substantial portion of the Sun (but never all of it) when it transits the face of the Sun, but Deimos would only look like a big sunspot in a telescope.

Orbit 6788 – Two Shadows

Orbit 6788, which observed the Phobos eclipse on September 13, 2000 at 15:14:43 Mars time, shows two shadows as shown in the picture below.  Because they are near the terminator, I increased the brightness and contrast of these images so that you can see them easier.

Phobos is indicated with “P->”, and the other shadow is indicated with the question mark.  The latitudes and longitudes are those for the center of the MOC swath, not for either shadow.  The 9.0% value in orbit 6788 is the vertical position of the shadow expressed as a percentage of the height of the image from top to bottom.  The time in the orbit 6776 picture is for the center of the scan, and the time in the orbit 6788 picture is the time that the eclipse was under the camera, which is 9.0% of the image scan time from start to stop.

The appearance of craters depends on how they are illuminated, and that varies from orbit to orbit.  Therefore, several reference orbits should be observed before a firm conclusion is made, and a set of these are presented in the next section reduced in scale.  The Phobos shadow in orbit 6788 above is larger and more diffuse than the one near the equator in orbit 5554 presented earlier.  This is a projection effect caused by the nearness of the shadow to the South Pole, and I’ll show other examples in orbits 6706 and 6624 later in this article.

The fact that there are two shadows in these images for orbit 6788 is a mystery.  A similar but possibly different mystery is why orbit 6706 also shows two shadows.  It is different because the extra shadow is a long extended one.  Orbit 6706 will be exhibited and discussed later in this article.  But first, let’s look at the same area of the surface in other orbits that we call reference orbits because they occur after orbit 6788 and do not show any shadows.

Did Malin Space Science Systems Censor Data?

The MOC is designed to photograph a mapping swath during the day lit portion of every orbit.  Many orbits are missing from the data set, and a complete analysis of missing orbits would require another article.  Other swaths are present in part, and the missing portion of the swath is blacked out.  I call those blacked-out portions “censored” for lack of a better term, and it may be an unfortunate choice of words because I can see how it could be misunderstood.  I don’t mean that I think that the missing information would be useful if we could see it or that there was anything on the ground that MSSS wanted to hide from public view.  I’m sure that there are technical reasons why the “censored” data was blacked out, and my guess as to what may have caused these technical reasons are given in the last paragraph in this section.

I find it curious that there are 56 consecutive mapping swaths missing or censored from June 5 to June 9, 2000.  (These swaths would be in the missing sequence of 121 consecutive images of any kind.)  The last good wide-angle mapping swath before this image gap was for orbit number 5561 (Image number m1600297) on June 5, 2000 from 08:59:49 to 09:57:46, and the next good wide-angle mapping swath after this gap was for orbit number 5617 (Image number m1600465) on June 9, 2000 from 22:48:14 to 23:46:11.  Orbit 5593 (= 5554 + 39) should have had a shadow of Phobos, but it is missing from the data set.  This may not be relevant, but I noticed that the top 40% of image m1600560 (orbit 5636) for June 11, 2000 is blacked out.  This was not a problem for me because the shadow was at 46.6% from the top.  Nevertheless, I could not see anything south (above) of 40%.

Not only wide-angle swaths are missing.  The following Image numbers in this time frame are missing from the data set or censored (blacked out) or contain errors and are unreadable.

Missing or Censored
Image Sequence Numbers

Number of Missing
Images in Gap

Number of Images
Present Between Gaps

m1600303 – m1600306

4

1

m1600308 – m1600309

2

2

m1600312 – m1600313

2

4

m1600316 – m1600317

2

8

m1600326 – m1600327

2

2

m1600330 – m1600331

2

3

m1600335 – m1600336

2

7

m1600344 – m1600464

121

 

I’d like to give MSSS the benefit of the doubt, but this pattern does appear to be more methodical than random.

In looking for more reference orbits at similar longitudes to compare with orbit 6788, I found it curious that quite a few of them were either missing or partially blacked out with a notation of “Errors” in the image header in the data quality description field.  In these instances, the blacked out portion of the images was always at the top (south end) of the image where we wanted to see the surface.  The MGS spacecraft flies over the same longitude (approximately) ever 12 or 13 orbits, so I looked at orbits 6801, 6814, 6826, 6839, 6851, 6864, 6876, 6889, 6902, 6914, and 6927, and these images are shown below.

Three of the orbits in this list are absent, and four of them are censored (blacked out).  There are many other missing orbits and blacked-out images in the data set, and a comprehensive analysis does not seem to be worth the effort at this time.

Allow me to speculate as to why some orbits are missing and others are censored.  Suppose the mission control people wanted to point the spacecraft’s cameras away from Mars from time to time to look at a comet.  If they did so, the data would not belong in the mapping swath data set, so those orbits would be missing from the data set.  Suppose that when they point the camera back towards Mars, the camera’s point of view does not reach its designated look angle until somewhere in the middle of a wide-angle swath.  It would make sense to censor that portion of the swath before the camera reached its designated direction while it was moving into position.  If that is true, then the censorship doesn’t mean there is anything on the surface of Mars that the mission control people want to hide from the public.  Rather, they just want to keep the published data set pure with only surface images of Mars, and any off-Mars peeks at the celestial sphere don’t belong.

Orbit 6706 Also Has Two Shadows

In the following pictures the shadow of Phobos is identified in orbit 6706 (= 6788 – 82) with “P->”.  The other “shadow” is the long dark inclined streak above it that is identified with the question mark.  This is either (1) a transient surface feature such as a dust or smoke plume or (2) the shadow of something in space that is moving rapidly from right to left (since the camera scans downward), or (3) the smoky trail of a bolide that skipped through the atmosphere.  It can’t be a cloud because a cloud should be white and appear differently in the red-filtered and blue-filtered pictures.

This can’t be the shadow of anything in orbit around Mars, unless it is very low in altitude because its length is much too long, judging from the length of the Phobos shadow.  If it is a space body, it could be something in a retrograde (clockwise) orbit around the Sun that happens to be passing in front of Mars, because Mars moves from left to right (in these upside-down pictures) in its counter-clockwise orbit.  However, this “shadow” has striations in the red-filtered image and a central gap in both the red and blue-filtered images.  The shadow of something in space moving across the field of view should not have any structure to it unless it is a tumbling flat disk.  So, the most likely explanation is that this “shadow” is a transient surface feature or a bolide trail.

 

The outside pictures for orbits 6681 and 6744 are “before” and “after” pictures of the same place on Mars.  Notice that they are displaced to the left compared to orbit 6706.  (That means nothing except you need to compensate when you compare the outer pictures to the inner pictures.)  In all three of the red-filtered pictures, you can see a small dark but faint streak crossing the bottom-left of a crater that just happens to be aligned with the axis of the Phobos shadow in orbit 6706 (red filter).  The streak is above and to the right of the shadow of Phobos in that picture.  The fact that this streak is absent in the blue-filtered picture is proof that it is a surface feature, not a shadow.

I found that orbits 6705, 6718, and 6719 were missing and that orbits 6693 and 6731 were blacked out.  So, orbit 6681 (= 6706 – 25) was the latest orbit before orbit 6706 and orbit 6744 (= 6706 + 25 + 13) was the earliest orbit following orbit 6706 that covered the same land area.  But even orbit 6681 is not complete.  It is truncated, and the bottom 60% of the swath is missing.  Even so, there seems to be nothing wrong with the top 40%, so I used it in the illustration above.

Conclusion

This study has not proved anything except that Malin Space Science Systems has not published sufficient data to rule out the hypothesis that Phobos may have escaped Mars orbit on or about July 2, 2001, when the recent global Martian dust storm in the 90ºW hemisphere started.  (It started in the other hemisphere on June 26.)  This July 2 date is interesting because it just so happens that two recent observations of Phobos were made visually on June 29 by Jeff Medkeff and with a CCD camera on July 1, 2001 by Don Bruns.  See The Phobos Mystery Continues.  It also seems fair to ask MSSS to explain the extra shadows in orbits 6706 and 6788 and the missing 55 consecutive mapping swaths from June 5, 2000 to June 9, 2000.

Exploring the MOC Raw Images Yourself

The Mars Global Surveyor MOC image links are arranged by orbit in http://ida.wr.usgs.gov/orb_page.html.  Unfortunately, you don’t know the orbit number until you open the corresponding browse page, which is two clicks away from this page.  This page is an array of links to Mapping Subphase Image lists named “m12345”, i.e., “m” followed by a 5-digit number.  When you click on one of those links, you get a list of up to 100 MOC image number links to an image’s browse page, and it is named “m1234567” (“m” followed by 7 digits).  The sub-phase list gives the center latitude and longitude and the resolution.  The wide-angle images have resolutions on the order of 6500 meters per pixel.  There are many more high-resolution images than wide-angle images.

Beginning with orbit 1098 the wide-angle images come in pairs; the first is the red-filtered image, and the second is the blue-filtered one.  You won’t know the orbit number until you open the browse page.  This page has lots of technical information and links to the jpeg image itself.  The image is shown in a thumbnail size in the lower-left corner of this browse page.  Click on this thumbnail image or the display button to get to the actual raw MOC image.  The image is first displayed in a reduced format.  Move your mouse to the lower right-hand corner of this reduced image, and (eventually) a magnifier button will appear.  Click on that button to get the raw image at 100% of its original size.

To get the start and stop times and the filter color, you must download the image file by clicking the download link in the browse page and reading the text header.  Actually, all you need is the header; so after you click on the download link, just click the stop button on your browser as soon as you see the header on your monitor.  That will save the time it would take to download the entire image.

The following is a complete list of all the MGS orbits that I found that have shadows of Phobos in them, together with their browse page links, the date, start and stop times, and the position of the shadow as a percentage of the distance from start to stop (South to North).  The time of each eclipse is given by the following formula:

Eclipse time = Start time + (shadow percentage) x (Stop time – Start time).

I think I may have found all of the Phobos shadow images in this data set, but I don’t guarantee it.

Browse pages with links to Images With Shadows: Orbit Date       Start    Stop     Shadow at

http://ida.wr.usgs.gov/html/m02003/m0200313.html 1098 1999/06/06 18:10:59 19:08:55 25.5%

http://ida.wr.usgs.gov/html/m02009/m0200934.html 1137 1999/06/09 22:39:39 23:37:36 28.8%

http://ida.wr.usgs.gov/html/m02021/m0202117.html 1219 1999/06/16 15:26:18 16:24:15 31.5%

http://ida.wr.usgs.gov/html/m02033/m0203366.html 1301 1999/06/23 08:12:45 09:10:41 33.9%

http://ida.wr.usgs.gov/html/m02041/m0204117.html 1344 1999/06/26 20:31:08 21:29:05 33.7%

http://ida.wr.usgs.gov/html/m02046/m0204683.html 1383 1999/06/30 00:59:02 01:56:59 36.5%

http://ida.wr.usgs.gov/html/m03005/m0300527.html 1426 1999/07/03 13:17:22 14:15:19 36.9%

http://ida.wr.usgs.gov/html/m03011/m0301160.html 1465 1999/07/06 17:45:13 18:43:10 39.1%

http://ida.wr.usgs.gov/html/m03017/m0301751.html 1508 1999/07/10 06:03:28 07:01:25 41.6%

http://ida.wr.usgs.gov/html/m03023/m0302334.html 1547 1999/07/13 10:31:16 11:29:13 41.8%

http://ida.wr.usgs.gov/html/m03031/m0303111.html 1590 1999/07/16 22:49:26 23:47:23 42.3%

http://ida.wr.usgs.gov/html/m03037/m0303731.html 1629 1999/07/20 03:17:11 04:15:08 44.4%

http://ida.wr.usgs.gov/html/m03044/m0304460.html 1672 1999/07/23 15:35:17 16:33:14 45.0%

http://ida.wr.usgs.gov/html/m03050/m0305034.html 1711 1999/07/26 20:02:58 21:00:55 47.0%

http://ida.wr.usgs.gov/html/m03057/m0305735.html 1754 1999/07/30 08:21:02 09:18:59 47.9%

http://ida.wr.usgs.gov/html/m03069/m0306929.html 1836 1999/08/06 01:06:39 02:04:36 50.8%

http://ida.wr.usgs.gov/html/m03075/m0307517.html 1875 1999/08/09 05:34:14 06:32:11 52.6%

http://ida.wr.usgs.gov/html/m03075/m0307594.html 1879 1999/08/09 13:24:39 14:22:36 51.3%

http://ida.wr.usgs.gov/html/m04005/m0400593.html 1918 1999/08/12 17:52:24 18:50:20 53.3%

http://ida.wr.usgs.gov/html/m04012/m0401229.html 1961 1999/08/16 06:11:08 07:09:05 54.5%

http://ida.wr.usgs.gov/html/m04017/m0401793.html 2000 1999/08/19 10:39:20 11:37:16 56.2%

http://ida.wr.usgs.gov/html/m04024/m0402470.html 2039 1999/08/22 15:07:31 16:05:28 57.9%

http://ida.wr.usgs.gov/html/m04032/m0403239.html 2082 1999/08/26 03:26:13 04:24:10 59.0%

http://ida.wr.usgs.gov/html/m07001/m0700166.html 2164 1999/09/01 20:13:04 21:11:01 62.0%

http://ida.wr.usgs.gov/html/m07015/m0701507.html 2246 1999/09/08 12:59:54 13:57:50 64.8%

http://ida.wr.usgs.gov/html/m07020/m0702058.html 2285 1999/09/11 17:27:59 18:25:56 66.5%

http://ida.wr.usgs.gov/html/m07027/m0702727.html 2328 1999/09/15 05:46:40 06:44:37 68.0%

http://ida.wr.usgs.gov/html/m07034/m0703448.html 2367 1999/09/18 10:14:48 11:12:45 69.3%

http://ida.wr.usgs.gov/html/m07041/m0704165.html 2410 1999/09/21 22:33:29 23:31:26 71.0%

http://ida.wr.usgs.gov/html/m07047/m0704746.html 2449 1999/09/25 03:01:36 03:59:33 72.1%

http://ida.wr.usgs.gov/html/m08001/m0800120.html 2531 1999/10/01 19:48:20 20:46:17 75.3%

http://ida.wr.usgs.gov/html/m08019/m0801929.html 2613 1999/10/08 12:35:08 13:33:05 78.8%

http://ida.wr.usgs.gov/html/m08032/m0803290.html 2695 1999/10/15 05:22:04 06:20:00 81.3%

http://ida.wr.usgs.gov/html/m08053/m0805349.html 2777 1999/10/21 22:08:40 23:06:36 85.4%

http://ida.wr.usgs.gov/html/m08061/m0806110.html 2816 1999/10/25 02:36:49 03:34:45 87.6%

http://ida.wr.usgs.gov/html/m08070/m0807001.html 2859 1999/10/28 14:55:28 15:53:25 89.5%

http://ida.wr.usgs.gov/html/m08080/m0808051.html 2898 1999/10/31 19:23:39 20:21.36 91.8%

http://ida.wr.usgs.gov/html/m09016/m0901647.html 2980 1999/11/07 12:10:38 13:08:30 96.4%

http://ida.wr.usgs.gov/html/m12023/m1202369.html 4304 2000/02/23 16:15:27 17:13:24 96.4%

http://ida.wr.usgs.gov/html/m12026/m1202620.html 4347 2000/02/27 04:34:17 05:32:14 92.3%

http://ida.wr.usgs.gov/html/m13000/m1300081.html 4390 2000/03/01 16:53:06 17:51:02 89.3%

http://ida.wr.usgs.gov/html/m13003/m1300369.html 4433 2000/03/05 05:11:52 06:09:49 87.5%

http://ida.wr.usgs.gov/html/m13007/m1300731.html 4515 2000/03/11 21:58:57 22:56:54 83.5%

http://ida.wr.usgs.gov/html/m13009/m1300999.html 4558 2000/03/15 10:17:39 11:15:36 81.8%

http://ida.wr.usgs.gov/html/m13012/m1301221.html 4601 2000/03/18 22:36:32 23:34:29 80.7%

http://ida.wr.usgs.gov/html/m13015/m1301522.html 4640 2000/03/22 03:04:52 04:02:48 78.8%

http://ida.wr.usgs.gov/html/m13017/m1301758.html 4683 2000/03/25 15:23:41 16:21:38 77.1%

http://ida.wr.usgs.gov/html/m13020/m1302058.html 4726 2000/03/29 03:42:35 04:40:32 75.8%

http://ida.wr.usgs.gov/html/m14000/m1400014.html 4765 2000/04/01 08:10:53 09:08:50 74.1%

http://ida.wr.usgs.gov/html/m14003/m1400319.html 4808 2000/04/04 20:29:47 21:27:44 72.6%

http://ida.wr.usgs.gov/html/m14005/m1400511.html 4851 2000/04/08 08:48:43 09:46:39 71.4%

http://ida.wr.usgs.gov/html/m14007/m1400738.html 4890 2000/04/11 13:16:57 14:14:54 70.0%

http://ida.wr.usgs.gov/html/m14010/m1401025.html 4933 2000/04/15 01:35:56 02:33:52 68.3%

http://ida.wr.usgs.gov/html/m14012/m1401273.html 4972 2000/04/18 06:04:08 07:02:05 67.9%

http://ida.wr.usgs.gov/html/m14015/m1401526.html 5015 2000/04/21 18:23:06 19:21:02 65.9%

http://ida.wr.usgs.gov/html/m14017/m1401749.html 5054 2000/04/24 22:51:20 23:49:16 65.2%

http://ida.wr.usgs.gov/html/m14017/m1401790.html 5058 2000/04/25 06:42:00 07:39:57 64.4%

http://ida.wr.usgs.gov/html/m15000/m1500071.html 5140 2000/05/01 23:29:13 00:27:10 61.6%

http://ida.wr.usgs.gov/html/m15002/m1500272.html 5179 2000/05/05 03:57:31 04:55:28 60.9%

http://ida.wr.usgs.gov/html/m15002/m1500287.html 5183 2000/05/05 11:48:13 12:46:10 60.5%

http://ida.wr.usgs.gov/html/m15005/m1500561.html 5222 2000/05/08 16:16:30 17:14:27 59.2%

http://ida.wr.usgs.gov/html/m15007/m1500791.html 5265 2000/05/12 04:35:28 05:33:25 57.6%

http://ida.wr.usgs.gov/html/m15009/m1500982.html 5304 2000/05/15 09:03:44 10:01:40 56.9%

http://ida.wr.usgs.gov/html/m15011/m1501198.html 5347 2000/05/18 21:22:44 22:20:41 55.4%

http://ida.wr.usgs.gov/html/m15014/m1501437.html 5390 2000/05/22 09:41:40 10:39:36 53.9%

http://ida.wr.usgs.gov/html/m15016/m1501657.html 5429 2000/05/25 14:10:01 15:07:58 53.0%

http://ida.wr.usgs.gov/html/m15019/m1501909.html 5472 2000/05/29 02:28:58 03:26:55 51.4%

http://ida.wr.usgs.gov/html/m16000/m1600029.html 5511 2000/06/01 06:57:17 07:55:14 50.9%

http://ida.wr.usgs.gov/html/m16002/m1600263.html 5554 2000/06/04 19:16:17 20:14:14 48.9%

http://ida.wr.usgs.gov/html/m16005/m1600560.html 5636 2000/06/11 12:03:36 13:01:33 46.6%

http://ida.wr.usgs.gov/html/m16007/m1600737.html 5679 2000/06/15 00:22:36 01:20:33 44.8%

http://ida.wr.usgs.gov/html/m16009/m1600955.html 5718 2000/06/18 04:50:59 05:48:56 44.6%

http://ida.wr.usgs.gov/html/m16011/m1601129.html 5761 2000/06/21 17:10:01 18:07:58 42.9%

http://ida.wr.usgs.gov/html/m17000/m1700074.html 6050 2000/07/15 07:52:39 08:50:35 34.1%

http://ida.wr.usgs.gov/html/m17003/m1700303.html 6089 2000/07/18 12:21:28 13:19:24 33.7%

http://ida.wr.usgs.gov/html/m17005/m1700546.html 6132 2000/07/22 00:40:46 01:38:43 31.8%

http://ida.wr.usgs.gov/html/m17008/m1700803.html 6171 2000/07/25 05:09:37 06:07:33 31.3%

http://ida.wr.usgs.gov/html/m17010/m1701043.html 6214 2000/07/28 17:29:04 18:27:00 29.2%

http://ida.wr.usgs.gov/html/m18002/m1800232.html 6296 2000/08/04 10:17:26 11:15:23 26.6%

http://ida.wr.usgs.gov/html/m18006/m1800648.html 6378 2000/08/11 03:05:50 04:03:46 24.2%

http://ida.wr.usgs.gov/html/m18010/m1801051.html 6460 2000/08/17 19:54:17 20:52:14 21.7%

http://ida.wr.usgs.gov/html/m18014/m1801474.html 6542 2000/08/24 12:42:54 13:40:51 18.8%

http://ida.wr.usgs.gov/html/m18018/m1801895.html 6624 2000/08/31 05:31:37 06:29:34 16.1%

http://ida.wr.usgs.gov/html/m19003/m1900366.html 6706 2000/09/06 22:20:26 23:18:23 12.7%

http://ida.wr.usgs.gov/html/m19008/m1900876.html 6788 2000/09/13 15:09:30 16:07:26 09.0%

http://ida.wr.usgs.gov/html/m19014/m1901418.html 6870 2000/09/20 07:58:37 08:56:34 04.1%

 

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