IPB

Welcome Guest ( Log In | Register )

30 Pages V  « < 23 24 25 26 27 > »   
Reply to this topicStart new topic
Live Dust Devil?
MichaelT
post May 27 2005, 03:38 PM
Post #359


Member
***

Group: Members
Posts: 155
Joined: 18-March 05
From: Germany
Member No.: 211



Here is another nice DD from sol 496 (GIF-animation, 860 kB) and it leaves a dark track:


Obviously, the MER-team decided to take images at 100 sec intervals. So there won't be any additional images of the big one from sol 495 I'm afraid sad.gif

Michael
Go to the top of the page
 
+Quote Post
Tman
post May 28 2005, 07:41 AM
Post #360


Member
***

Group: Members
Posts: 877
Joined: 7-March 05
From: Switzerland
Member No.: 186



Sadly, it seems they've mistimed to modify their tactic. Probably they thought to have enought DD animations and no longer calculated with a variation.

Also maybe Spirit had to do something else. rolleyes.gif


--------------------
Go to the top of the page
 
+Quote Post
Guest_Sunspot_*
post May 28 2005, 03:25 PM
Post #361





Guests






Heres the JPL animation of the dust devil on sol 486

http://www.jpl.nasa.gov/missions/mer/images.cfm?id=1682

JPL .mov animation
Go to the top of the page
 
+Quote Post
dilo
post May 29 2005, 08:13 PM
Post #362


Senior Member
****

Group: Members
Posts: 2492
Joined: 15-January 05
From: center Italy
Member No.: 150



Cool!!!


--------------------
I always think before posting! - Marco -
Go to the top of the page
 
+Quote Post
Jeff7
post May 30 2005, 10:27 AM
Post #363


Member
***

Group: Members
Posts: 477
Joined: 2-March 05
Member No.: 180



QUOTE (Sunspot @ May 28 2005, 11:25 AM)
Heres the JPL animation of the dust devil on sol 486

http://www.jpl.nasa.gov/missions/mer/images.cfm?id=1682

JPL .mov animation
*


I wonder how big that thing got higher up - it cast a pretty large shadow around itself.
Go to the top of the page
 
+Quote Post
Tman
post May 30 2005, 11:54 AM
Post #364


Member
***

Group: Members
Posts: 877
Joined: 7-March 05
From: Switzerland
Member No.: 186



QUOTE (Jeff7 @ May 30 2005, 12:27 PM)
I wonder how big that thing got higher up - it cast a pretty large shadow around itself.
*

The DD's local time was 11.48 a.m. at the beginning of the animation. I guess that is nearly sun culmination. Does someone know the angle that sun currently appears by culmination at Gusev?

My guess for the DD's height is circa 170 meters.


--------------------
Go to the top of the page
 
+Quote Post
MichaelT
post May 30 2005, 04:38 PM
Post #365


Member
***

Group: Members
Posts: 155
Joined: 18-March 05
From: Germany
Member No.: 211



QUOTE (Tman @ May 30 2005, 11:54 AM)
The DD's local time was 11.48 a.m. at the beginning of the animation. I guess that is nearly sun culmination. Does someone know the angle that sun currently appears by culmination at Gusev?

My guess for the DD's height is circa 170 meters.
*


Currently, the sun's culmination height is about 88 at Sprit's location (I used Guide 8). So it's directly overhead at midday. Twelve minutes earlier the sun's elevation is about 87. So what we see is rather the horizontal extension of the dust devil projected onto the plain than its hight.

Michael
Go to the top of the page
 
+Quote Post
Tman
post May 30 2005, 06:18 PM
Post #366


Member
***

Group: Members
Posts: 877
Joined: 7-March 05
From: Switzerland
Member No.: 186



Thanks! This sun position makes sense by comparing the whole course of the shadow. If so the DD was sometimes very wide in its higher part or it had sometime a rolling shape. Maybe about 100 meters wide, but I'm unsure which part of the DD the JPL caption means "about 35 meters in diameter".


--------------------
Go to the top of the page
 
+Quote Post
dilo
post Jun 1 2005, 05:32 AM
Post #367


Senior Member
****

Group: Members
Posts: 2492
Joined: 15-January 05
From: center Italy
Member No.: 150



Last DD (Sol-501) seems very far and huge! Here NavCam details of the same position taken about 3 min apart (no DD enhancement, only some retouch in order to improve luminosity/contrast and reduce jpeg artifacts):

In the last frame, DD base is only 6 pixel (0.28deg) below horizon... I do not remember actual height of Spirit above the plain, but assuming 50m, the distance should be about 10 Km, so DD width is at least 350m ohmy.gif
Do someone can confirm these numbers or/and make enhanced version?


--------------------
I always think before posting! - Marco -
Go to the top of the page
 
+Quote Post
wyogold
post Jun 1 2005, 08:11 AM
Post #368


Member
***

Group: Members
Posts: 118
Joined: 14-March 05
Member No.: 195



QUOTE (dilo @ Jun 1 2005, 05:32 AM)
Last DD (Sol-501) seems very far and huge! Here NavCam details of the same position taken about 3 min apart (no DD enhancement, only some retouch in order to improve luminosity/contrast and reduce jpeg artifacts):
In the last frame, DD base is only 6 pixel (0.28deg) below horizon... I do not remember actual height of Spirit above the plain, but assuming 50m, the distance should be about 10 Km, so DD width is at least 350m  ohmy.gif
Do someone can confirm these numbers or/and make enhanced version?
*



Wow cool stuff. I hope they catch one of those that etch the huge tracks you can see from space.
Go to the top of the page
 
+Quote Post
MichaelT
post Jun 1 2005, 09:43 AM
Post #369


Member
***

Group: Members
Posts: 155
Joined: 18-March 05
From: Germany
Member No.: 211



QUOTE (dilo @ Jun 1 2005, 05:32 AM)
Do someone can confirm these numbers or/and make enhanced version?
*

Assuming an elevation of 50 m I get the same results. The enhanced version looks like this:

The dust in the left section does not belong to the big one which develops 100 s later.

Looks like a devilish day at Gusev Crater rolleyes.gif

The three large dd in frame 1 have diameters of 180, 160 and 260 m, approximately (see below).


Also very interesting is the change of brightness between frames 4 and 5. Using an enhancement level of 20 it becomes obvious that there are very week dd moving through, which are almost invisible otherwise.


Michael
Go to the top of the page
 
+Quote Post
AndyG
post Jun 1 2005, 09:45 AM
Post #370


Member
***

Group: Members
Posts: 588
Joined: 20-April 05
Member No.: 279



QUOTE (dilo @ Jun 1 2005, 05:32 AM)
In the last frame, DD base is only 6 pixel (0.28deg) below horizon... I do not remember actual height of Spirit above the plain, but assuming 50m, the distance should be about 10 Km, so DD width is at least 350m  ohmy.gif
Do someone can confirm these numbers or/and make enhanced version?
*


For the 16 degree field of view pancam, with 1024 pixels, I get 6 pixels equalling 0.09375 degrees.

A little trigonometry:

Horizon distance = SQRT((h*h)+(2*R*h))

...where h is the height and R the radius of Mars (3397000 metres). If an object appears "n" pixels below a distant (and assumed flat) horizon, then the distance "x" to that object is given by:

x = R*cos(A)+SQRT((R*R*cos(A)*cos(A))+(h*h)+(2*R*h))

...where A is 90+(16*n/1024) degrees.

So in this instance, if h is 50, then x is about 13.5 km. Gusev appears to be fairly flat, so the assumption feels about right.

Andy G
Go to the top of the page
 
+Quote Post
MichaelT
post Jun 1 2005, 11:44 AM
Post #371


Member
***

Group: Members
Posts: 155
Joined: 18-March 05
From: Germany
Member No.: 211



QUOTE (AndyG @ Jun 1 2005, 09:45 AM)
For the 16 degree field of view pancam, with 1024 pixels, I get 6 pixels equalling 0.09375 degrees.

Thanks for these equations smile.gif

The dd images used here are Navcam images (2nd character of the file name is "N") which have a field of view of ~45 degrees. Therefore the angle per pixel is 45/1024 px = 0.043945 /px.

Using that number for the calculation yields a distance of 8.5 km for the dust devil. Which is still close to 10 km.

Michael
Go to the top of the page
 
+Quote Post
AndyG
post Jun 1 2005, 12:05 PM
Post #372


Member
***

Group: Members
Posts: 588
Joined: 20-April 05
Member No.: 279



QUOTE (MichaelT @ Jun 1 2005, 11:44 AM)
Thanks for these equations smile.gif

The dd images used here are Navcam images (2nd character of the file name is "N") which have a field of view of ~45 degrees. Therefore the angle per pixel is 45/1024 px = 0.043945 /px.
*


Ah! Mea culpa! ;-)

Andy G
Go to the top of the page
 
+Quote Post
Mongo
post Jun 1 2005, 05:37 PM
Post #373


Member
***

Group: Members
Posts: 709
Joined: 13-June 04
Member No.: 82



So these 'dust-devils' can reach 300m in diameter, and according to this website, Martian dust-devils can reach nearly 8km in height.. That seems awfully large for a dust-devil. From what I can find on the Web, on Earth the largest dust-devils reach about 100m in diameter, and maybe 1km in height.


It does seem to be the rule that on Mars, everything is an order of magnitude bigger than on Earth.

Bill
Go to the top of the page
 
+Quote Post

30 Pages V  « < 23 24 25 26 27 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 4th August 2020 - 05:49 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.