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应该算是8月中旬的新闻了，随着 SETI@home 用上了新设备，搜索的效率大大提高了。
好久没算SETI了，估计现在就是用的新数据。
http://www.planetary.org/program ... thome_20060814.html
It has been two years now since the seven pronged multi-beam receiver was hoisted above the Arecibo radio telescope and installed in the Gregorian dome, 500 feet above the surface of the dish. During this time the new receiver had become an inseparable part of the regular operations at Arecibo, providing a new and indispensable resource for teams of scientists from around the world. But it was only two months ago that members of the SETI@home team headed down to Arecibo to join the fray. In seven intense days spent at the radio telescope Chief scientist Dan Werthimer and his colleagues completely overhauled the way SETI data is gathered at Arecibo, and ensured that SETI@home will henceforth enjoy the benefits of gathering data with the most advanced equipment anywhere in the world.
自七波束接收器安装到阿雷西博望远镜距地面500英尺的穹顶里已经有两年了。在此期间新的接收器已经成为阿雷西博常规操作不可分割的一部分，为来自全球的科学家小组提供新的、必不可少的资源。但是直到两个月前 SETI@home 的小组才加入到这在场争夺中。在射电望远镜热火朝天的干了7天，首席科学家 Dan Werthimer 和同事全面检查了阿雷西博收集的用于 SETI 的数据，并确定 SETI@home 今后将享用这全球最先进的设备收集的数据。
Unlike ordinary radio telescope receivers, which point and listen to a single point in the sky at any given time, Arecibo's new multi-beam receiver can point to seven different points simultaneously. Its seven receivers, arranged in a hexagon, operate independently, each collecting its own data separately from the others from a slightly different location in the sky. For many astronomers, interested in studying specific locations in the sky for extended periods of time, the multi-beam receiver offers no particular advantages. But for those interested in scanning the entire sky, the multi-beam arrangements is ideal: by pointing at seven points simultaneously, the new receiver can cover the entire surface of the sky many times faster than a traditional single beam.
与普通的射电望远镜接收器在一个给定的时间只能指向并监听天空中的一个点不同，阿雷西博的新多波束接收机能同时指向7个不同的方向。7个接收器环列成六边形，独立的操作，各自从空中稍有不同的地点收集自己的数据。许多天文学家对长期研究空中的特殊区域都很感兴趣，多波束接收器不提供这方面的特殊便利。但是对那些想进行全天搜索的人来说，多波束阵列是很理想的：同时指向7个方向，新的接收器扫完整个天空将比传统的单波束接收器快许多倍。
And so it was that astronomers from several different fields joined forces and created the ALFA (Arecibo L-band Feed Array) consortium, charged with operating the new receiver. Each of the groups making up the consortium has its own scientific focus. One group is interested in mapping the distribution of hydrogen in the universe, another in the location of pulsars, and yet another is studying the structure of our galaxy, the Milky Way. The SETI group, of course, is searching for an intelligent signal emanating from somewhere in the universe. But all members of ALFA are united by a shared goal: to use the largest and most sensitive radio telescope in the world to conduct systematic surveys of the entire sky. In the competitive environment that governs telescope time allotments, no group by itself would be granted sufficient telescope time to conduct an efficient sky survey. But there is strength in numbers: working together, the ALFA consortium is granted as much as one third of all the observation time at Arecibo.
因此来自不同领域的一些天文学家组建了 ALFA 协会（阿雷西博 L-波段提供队列 Arecibo L-band Feed Array），承担对新接收机的操作。每一个小组为协会拟订各自的关注方面。某个小组对绘制宇宙中氢的分布图感兴趣，另一个则对定位脉冲星感兴趣，还有的在研究银河系的结构。SETI小组当然是对寻找宇宙中智慧信号的发射地感兴趣。不过所有的ALFA成员是因共同的目标结合在一起的：用世界上最大、最灵敏的射电望远镜对整个天空实施系统的调查。相互竞争望远镜的支配时间，没有小组能得到充足的使用时间实施直接的全天区调查。但是成员们的共同努力使ALFA协会获得了阿雷西博差不多三分之一的观测时间。
Because it is so hard to acquire sufficient telescope time for a sky survey, SETI observations at Arecibo were conducted up to now in the in the piggy-back mode. This means that the SETI receiver was perched permanently above the Arecibo dish at the base of the aging line feed antenna. Whichever point in the sky the telescope happened to be pointed at, that's where the SETI receiver would listen for intelligent signals. Over time, even without being granted dedicated telescope time, the piggy back SETI receiver managed to scan the entire sky visible from Arecibo.
因为很难得到充足的望远镜使用时间进行全天调查，如今SETI在阿雷西博的观测采取的是一种附加式的模式。也就是说 SETI 的接收器永久的占据着阿雷西博碟型天线上老化的线性馈源的底部。任何一个指向天空时望远镜也就对准了那里，也就是 SETI 接收机将要监听智能信号的地方。随时间流逝，即使没有获得专门的望远镜时间，附加式的 SETI 接收器也能扫描完整个天空。
While this arrangement made the best of a difficult situation, it was hardly ideal. Subject to the random vicissitudes of piggy-backing, a complete survey of the sky visible from Arecibo would take several years, and it was, furthermore, very uneven. Certain segments of the sky, interesting to some astronomers for their own reasons, were covered many times over before other locations were observed even once. This is a very inefficient way to conduct a SETI survey whose underlying assumption is that a signal from E.T. may come from anywhere in the sky.
然而这种安排也有不理想的地方。附加模式受随机变迁的制约，用阿雷西博完成整个天空的调查将花费数年的时间，并且非常的不均匀。一些天文学家出于自己的原因对某些确定的天区很感兴趣，会在那里花许多时间一遍又一遍的观察。这对于假定E.T.的信号可能从任何一个方向过来的SETI调查是非常低效的。
Now, with the ALFA consortium operating the multi-beam receiver, things have become much simpler for SETI observers. Since all members of the consortium are interested in conducting an efficient sky survey, the multi-beam receiver will be scanning the entire sky systematically and relatively quickly. Technically, since Werthimer's group will at no time be controlling the telescope, SETI will still be "piggy backing" on the observations of others. But whereas previously SETI was forced to rely on the random meanderings of the telescope across the sky, it will now be able to look for signs of alien intelligence in a systematic survey of the entire sky. If before SETI was merely a passenger, going along for the ride, by joining forces with the ALFA consortium SETI has moved much closer to the driver's seat of observations.
现在，ALFA 协会控制着多波束接收器，对SETI观测来说事情变得非常简单了。既然协会的全体成员都对实施一次有效的天空搜索感兴趣，多波束接收器将会系统、而且相对快速的扫描整个天空。从技术上讲，由于 Werthimer 的小组没有控制望远镜的使用时间，SETI 仍将附加在其他的观测上。然而以前的 SETI 只能依赖于望远镜在空中随机的漫步，如今可以系统地调查整个星空寻找外星智能的信号。如果说以前的 SETI 只是一个随车旅行的乘客，那么同 ALFA 结合在一起后 SETI 离司机的位置更近了。
This increases the efficiency of the SETI@home sky survey enormously, and would in itself have made the transition to the multi-beam receiver a giant step forward for SETI@home. But the benefits of the move do not end here: there are several additional reasons why collecting data on the multi-beam receiver represents a several-fold increase in the power and sensitivity of the search.
这些变化巨大的增进了 SETI@home 调查天空的效率，使 SETI@home 向前迈进了一大步。好处还不止这些：多波束接收器使搜索的能力和灵敏度提升了数倍。
One factor is that unlike the old line feed antenna, which was hanging by itself, exposed to the tropical elements, the multi-beam receiver is located inside the distinctive-looking Gregorian dome. This is significant because of the unique geometrical features of the Arecibo telescope: whereas most radio dishes are parabolic in shape, the Arecibo dish is a giant half-sphere dug into the ground. Parabolic dishes have the advantage that they point their beams to a single point at their focus, creating a clear and strong signal. A sphere, in contrast, concentrates its beam to a line – which is why a "line feed" antenna was originally used at Arecibo.
与老的线性反馈天线暴直接露在热带环境中不同，多通道接收器安放在富有罗马特色的穹顶中。这非常重要，由于阿雷西博望远镜的独特几何结构：尽管绝大多数的射电望远碟面都是抛物面型的，而阿雷西博的碟面是在地上挖出的一个巨大半球。抛物面碟面的优点是能将波束在它的焦点处汇聚到一个单一的点，产生一个清晰、强力的信号。球形的则不同，它会把波束汇聚到一条线上——这就是为什么阿雷西博先前使用的是“线反馈”天线。
When using a line feed, telescope operators produce a unified signal by adding up the different parts of the signal, but the results are never as strong and clear as they are with a parabolic dish. The Gregorian dome, due to its unique geometrical shape, focuses the signal reflected by Arecibo spherical dish one a single point inside the dome. In effect, the Gregorian dome transforms Arecibo's spherical dish into the equivalent of a parabolic dish.
使用线形馈源时，操作者产生一个标准信号叠加到信号的不同部分，但是结果从不会像使用抛物面碟面得到的那样强大、清晰。“罗马穹顶”由于它独特的几何外形，将阿雷西博球形碟面反射来的信号聚焦到它内部的一个点上。效果上“罗马穹顶”将阿雷西博的球形碟面变成了抛物面形碟面。
To take advantage of this, the receiver has to be positioned at the focus point inside the dome. The dome therefore contains several such receivers, each with different characteristics, which rotate around, taking turns at the focal point. The multi-beam receiver is the most recent addition to this exclusive club, and it provides SETI scientists with a level of sensitivity that could never be achieved with the line feed antenna.
为利用这一点，接收器必须安放在穹顶内的焦点上。因此穹顶内包含了数个这样的接收器，每一个有着不同的特性环列在周围，轮流占据焦点。多波束接收器是其中最新的一个成员，它将为 SETI 的科学家提供使用线反馈天线所永远无法企及的灵敏度。
Another advantage is, most obviously, that the multi-beam antenna looks at seven different points simultaneously. This makes it possible to cover the entire sky far more quickly than when working with a traditional single-beam receiver. When combined with the fact that all ALFA members are interesting in conducting a systematic sky survey, the result is far faster and more even coverage of the heavens.
另一个很明显的优势，多波束天线在同一时刻观察着七个不同的方向。这就使得它能够比传统的单波束接收机更快的覆盖整个天空。同时由于全体 ALFA 成员都旨在实施一次系统的全天勘查，结果就是更快、更均匀的覆盖天空。
Then there are the advanced characteristics of the seven receivers themselves. Each of them is about 5 times more sensitive than the old receiver, located at the base of the line feed. Add to that the fact that the new version of the SETI@home client program -- the one users run on their computers – is also 5 times more sensitive than the old program. Together, the new receiver and the new software bring about a 25-fold increase in sensitivity for SETI@home!
第三个优点就是七个接收器本身。每一个的灵敏度都是原来线馈源底部老接收器的5倍以上。新的 SETI@home 的客户端，也就是用户们正在自己的机器上运行的程序，也比原来的老程序提高了5倍以上的灵敏度。新的接收器和新的程序加起来给新的 SETI@home 带来了25倍的灵敏度提升！
The multi-beam receiver is also uniquely suited for resolving one of the nagging problems of modern radio-telescopy: screening out radio frequency interference (RFI). It is an unavoidable fact that the radio frequencies in which radio telescopes listen for faint signals from the sky are flooded with not-at-all faint man-made radio signals that originate here on Earth. Separating RFI from true signals from the sky is a persistent challenge for all radio-telescopic observations, including SETI.
多波束接收器也是唯一适合解决现代射电望远镜的一个通病：滤掉电波干扰。这是一个无法回避的事实，射电望远镜所监听的来自太空的微弱信号淹没在地面的“强大”人造电波中。将真实信号从频率干扰中分离出来是包括 SETI 在内的所有射电观测所面对的长期挑战。
In this, however, a multi-beam receiver offers a unique advantage. Since each of the beams is looking at a different section of the sky, then a true signal, coming from space, would show up in only one of the receivers. Therefore, if a signal appears on more than one of the receivers, it is a sure sign that it is not coming from space at all, but most likely from the area around Arecibo. This simple screening of signals is an enormous help to the SETI@home team, by keeping out of consideration a mass of RFI signals, which might otherwise be subject to careful and time-consuming analysis.
无论如何多波束接收器提供了独一无二的优越条件，既然每一个波束都对着天空的不同部分，那么一个来自太空的真实信号只会出现在一个接收器中。如果一个信号出现在不止一个接收器中，可以肯定它不是来自太空，很有可能来自阿雷西博周围的地区。
With all these advantages in mind, the SETI@home team, comprising Dan Werthimer, Jeff Cobb, and Josh Von Korff, headed down to Arecibo to make the switch. First, they disconnected the old faithful SETI receiver that was attached to the line feed, and then they set about establishing the connection between the SETI@home network and the multi-beam receiver.
考虑到这些优点，SETI@home 的团队包括 Dan Werthimer、 Jeff Cobb 和 Josh Von Korff，来到阿雷西博作切换的工作。首先，他们拆下了附加在线馈源底部、SETI@home 忠实的接收器，随后着手建立 SETI@home 同多波束接收器的网络连接。
A chief component of this transition was the brand new data recorder, designed and built by Dan Werthimer and Aaron Parsons, with software designed and implemented by Jeff Cobb. Despite its modest name, the so called "recorder" is, in a way, the brains of the SETI observations. It does, of course, record the data, and unlike the old recorder, which listened and recorded on a single channel, the new recorder is tuned to no less than 14 channels. This means that it records the seven receivers that comprise the "multi-beam" separately, each of them at 2 different polarizations.
此次转换中最重要的部分是全新的数据记录仪，由 Dan Werthimer 和 Aaron Parsons 设计、制造；Jeff Cobb 设计并执行程序。尽管名字朴实，就叫“记录仪”，但某种程度上它是 SETI 观测的大脑。它就是记录数据的，和老的只能监听、记录单一通道的记录仪不同，新的记录仪被调整到不少于14个通道。这意味着它可以分别记录组成“多波束”的7个接收器，每个接收器有两个不同的极化。
But the recorder has other responsibilities as well. It is, for instance, in constantly monitoring the automated ongoing transmissions at Arecibo, reporting which of the telescope's receivers is currently at the focal point, the frequency of the current observations, and where the telescope is pointing. If the multi-beam receiver is not at the focus, or if for other reasons the telescope is not generating data relevant for SETI@home, the recorder immediately suspends its recording operations. In fact, explains Jeff Cobb, a good part of his time at Arecibo was spent working closely with the telescope's technicians on integrating the recorder into Arecibo's network, and making sure that the communications flow smoothly.
然而记录仪最好还能负担点儿其他任务。事实如此，举个例子：不断的监视阿雷西博正在进行的自动传送，报告望远镜的哪个接收器正处在焦点上，当前观测的频率，望远镜正指向什么方向。如果多波束接收器不在焦点上，或者由于其他原因望远镜没有产生于 SETI@home 相关的数据，记录仪会立刻暂停记录操作。实际上，Jeff Cobb 解释道，他在阿雷西博最美妙的一段时间就是同望远镜的技术员们一同废寝忘食的将记录仪融入到阿雷西博的网络中，并确信通信流平稳。
Because all the members of the ALFA consortium share an interest in efficiently surveying the sky, the multi-beam receiver generally does not dwell on a single point for long. But on the occasions when this does happen, the recorder is programmed to take advantage of the situation. Normally, the SETI recorder is listening for signals at a band centered 1420 MegaHerz (MHz). But when the telescope is dallying at a specific point in the sky, there is no point in recording on a single frequency for an extended period of time. Instead, the recorder will begin listening at other, neighboring frequencies, jumping to 1422.5 MHz, 1425 MHz, etc, on one side, and to 1417.5 MHz and 1415 MHz on the other. Overall there are 21 different frequencies the recorder can tune into given sufficient time, and who knows? Maybe E.T.'s signal is being delivered in one of them.
由于全体 ALFA 协会的成员都对有效的调查天空感兴趣，多波束接收器通常不会在一个方向上仔细研究。不过一旦这种情况发生，记录仪将按既定程序利用这种情形。SETI 接收器正常监听的中心频率是1420 MHz。当望远镜在空中某个特定方向上停了下来，在一个频率上记录一大段时间就没什么用处了。取而代之的是记录仪将开始跳到邻近的频率监听，如1422.5 MHz、1425 MHz……1417.5 MHz、1415 MHz……。在充足的时间里记录仪总共能收听21个不同的频率，谁知道呢？或许 E.T. 的信号就包含在其中。
Overall, during their week at Arecibo Wertheimer, Cobb, and Von Korff put in the pieces that will make possible an enormous leap forward in the efficiency and sensitivity of SETI@home. And in the very near future, SETI@home users will begin processing data collected by Arecibo's cutting-edge multi-beam receiver.
总之，在阿雷西博的几周里 Wertheimer、Cobb 和 Von Korff 打的补丁将为 SETI@home 在效率和灵敏度方面带来一次巨大的飞跃。很快，SETI@home 的用户就可以处理由阿雷西博的利刃——多波束接收机收集的数据了。
[ Last edited by Rojer on 2006-9-5 at 19:21 ] |
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