I asked Joe Chavez at Sandia National Labs what was contained in the single text file Sentinel outputs from the external video grabber.<\/p>\n
It has this basic format:<\/p>\n
From the Bolide of March 23, 2008<\/p>\n
Event time: Sat 2008\/03\/22 04:26:41.04<\/p>\n
-30\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 156.8\u00a0\u00a0 338.0
-29\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 156.8\u00a0\u00a0 338.0
-28\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 156.8\u00a0\u00a0 338.0
—- SNIP —-
233\u00a0 1602\u00a0\u00a0 36538\u00a0\u00a0 226.4\u00a0\u00a0 329.6
234\u00a0 1595\u00a0\u00a0 34884\u00a0\u00a0 225.4\u00a0\u00a0 330.2
235\u00a0 1574\u00a0\u00a0 33285\u00a0\u00a0 224.5\u00a0\u00a0 330.7
236\u00a0 1581\u00a0\u00a0 31824\u00a0\u00a0 223.6\u00a0\u00a0 331.3
237\u00a0 1539\u00a0\u00a0 30273\u00a0\u00a0 222.5\u00a0\u00a0 331.9
238\u00a0 1577\u00a0\u00a0 28940\u00a0\u00a0 221.4\u00a0\u00a0 332.3
239\u00a0 1557\u00a0\u00a0 27557\u00a0\u00a0 220.3\u00a0\u00a0 332.8
240\u00a0 1582\u00a0\u00a0 26090\u00a0\u00a0 218.9\u00a0\u00a0 332.9
241\u00a0 1592\u00a0\u00a0 23868\u00a0\u00a0 217.2\u00a0\u00a0 333.3
242\u00a0 1636\u00a0\u00a0 23007\u00a0\u00a0 215.7\u00a0\u00a0 333.3
243\u00a0 1685\u00a0\u00a0 21843\u00a0\u00a0 214.1\u00a0\u00a0 333.4
244\u00a0 1702\u00a0\u00a0 21038\u00a0\u00a0 212.6\u00a0\u00a0 333.6
245\u00a0 1708\u00a0\u00a0 19880\u00a0\u00a0 211.1\u00a0\u00a0 333.6
246\u00a0 1760\u00a0\u00a0 18637\u00a0\u00a0 209.6\u00a0\u00a0 333.6
—- SNIP —-<\/p>\n
299\u00a0\u00a0\u00a0\u00a0 6\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 164.1\u00a0\u00a0 342.0
300\u00a0\u00a0\u00a0\u00a0 9\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 164.1\u00a0\u00a0 342.0
301\u00a0\u00a0\u00a0\u00a0 3\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 164.1\u00a0\u00a0 342.0<\/p>\n
Joe informed me:<\/p>\n
The first column shows frame counts, so each row represents about 1\/30th of a second. \u00a0The recording begins 30 frames (one second) before the system is triggered. \u00a0The time stamp corresponds to the trigger time.<\/p>\n
The second column shows the number of pixels that were above the threshold value.<\/p>\n
The third column is a measure of the total amplitude and is computed by summing all pixel values above threshold. \u00a0Since this value may change depending on what hardware you use, you will need to calibrate it against a known light source. \u00a0We have done this by uncovering the shadow of the full moon over the sentinel camera and recording the amplitude response of the sentinel event. \u00a0If you measure the amplitude response of the full moon to be XM, you can calculate the magnitude of any event of amplitude X with following formula:<\/p>\n
Magnitude = -12.6 \u2013 2.5 * log10( X \/ XM )\u00a0 <\/p>\n
This assumes that the magnitude of the full moon is \u201312.6<\/p>\n
The fourth column lists the X coordinate of the centroid of the event, in pixel units.<\/p>\n
The fifth column lists the Y coordinate of the centroid of the event, in pixel units.<\/p>\n
I have a request in to find out if the new WSentinel (internal video card) light data file uses the same equation for magnitude estimates.<\/p>\n
Update: September 04, 2010 17:42:24<\/p>\n
Dick Spalding responded to my WSentinel inquiry:<\/p>\n
Jeff,<\/p>\n
Regarding your magnitude question, I think the scaling for the new video card system should be the same as for the Sentinel box systems. However, you should be aware that for very bright events, the camera’s auto-iris feature will begin to reduce lens aperture, thus reducing the apparent brightness of the event.\u00a0 I don’t believe the full Moon causes the iris to be reduced, since planet brightness seems to be the same with or without the full Moon present.\u00a0 Iris control is based on total light on the camera’s CCD chip.\u00a0 So, a bright nearby light could potentially affect sensitivity by partially closing the iris.<\/p>\n
Also, these HiCam HB-710E cameras have a built-in automatic gain control (AGC), which increases electronic gain as the scene becomes darker. For the typical dark sky, the gain is at the maximum permitted by the screwdriver AGC setting on the camera back.\u00a0 Turning that setting to its maximum clockwise position gives the camera maximum sensitivity.\u00a0 However, the resulting electronic noise produces an image with lots of “snow”, which forces trigger thresholds to be set higher.\u00a0 Cameras that we ship usually have their AGC control backed off to a level that puts the snow below the default trigger threshold.\u00a0 At that setting, I don’t think the presence of the full Moon causes the electronic gain to be reduced. Whether that’s true could be tested by lowering the threshold until random triggering on the snow begins to occur on a dark sky, then repeating with the full Moon in view.\u00a0 I have not done that test.<\/p>\n
Dick Spalding<\/p>\n","protected":false},"excerpt":{"rendered":"
I asked Joe Chavez at Sandia National Labs what was contained in the single text file Sentinel outputs from the external video grabber. It has this basic format: From the Bolide of March 23, 2008 Event time: Sat 2008\/03\/22 04:26:41.04 -30\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 156.8\u00a0\u00a0 338.0 -29\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 156.8\u00a0\u00a0 338.0 -28\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0 156.8\u00a0\u00a0 338.0—- … Continue reading “Sentinel Magnitude light output file”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[43],"tags":[],"class_list":["post-364","post","type-post","status-publish","format-standard","hentry","category-video-analysis"],"_links":{"self":[{"href":"https:\/\/bcmeteors.net\/index.php?rest_route=\/wp\/v2\/posts\/364","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bcmeteors.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bcmeteors.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bcmeteors.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bcmeteors.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=364"}],"version-history":[{"count":0,"href":"https:\/\/bcmeteors.net\/index.php?rest_route=\/wp\/v2\/posts\/364\/revisions"}],"wp:attachment":[{"href":"https:\/\/bcmeteors.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=364"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bcmeteors.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=364"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bcmeteors.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=364"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}