Subject: [Fwd: Re: CloudSat] From: Darrel Emerson Date: Tue, 24 Aug 2004 08:55:48 -0700 To: soliver Permission for Exhibit B. Note the: "You are of course most welcome to circulate my 1996 stuff and post it on the web." in the 2nd para. Cheers, Darrel. -------- Original Message -------- Subject: Re: CloudSat Date: Tue, 10 Aug 2004 15:59:59 +0100 From: johnpon To: Darrel Emerson References: <008e01c28509$ad5c4360$910928d5@oemcomputer> <4117F7BE.7040301@nrao.edu> Dear Darrel, Thanks for yours. I heard from Dick about a month ago that the cloud radar was raising its ugly head again and I did as a result look at my file thereon. But he didn't tell me that there would be five satellites marching in close file. It never occured to me that that might be the way to solve what I thought would be their insurmountable problem, notably how to make a fast high-power low-noise TR switch at 94GHz.. I remember asking them at Geneva what they proposed to do about a TR switch and they had no idea. I told them its the crucial item and that if they can't make a TR they can't have the radar. Obviously they don't know how to make a TR and have been forced to go Bistatic. They will transmit from one (or two?) satellite(s) and receive on the others. I guess I didn't think big enough - well just have another satellite! You are of course most welcome to circulate my 1996 stuff and post it on the web. Dick sent me a copy which appeared on my screen with his annotation. If you'd like a clean copy I could easily print one out for you. He found a typo which needs to be corrected to before its is circulated. When I read through it again I saw that I had omitted my thoughts about the radar PRF and how it needs to be adjusted. I spelt out my thoughts to Dick in an email I sent him on 5th July. and I asked him to somehow add them to my original note. In case he didn't forward it to you I will forward it immediately. The cloud radar people will need to be continuously adjusting their PRF to ensure that the echoes from the clouds in the troposphere down to ground level, fall within the time-base gaps between their transmitted pulses. The range to the ground changes because 1. the Earth is an ellipsoid not a sphere, 2. the orbit has finite eccentricity, 3. ground topography. The necessary adjustments can be made either in a way friendly to radio astronomy or in a way hostile to radio astronomy. The friendly way is to make gentle smooth and phase continuous changes to the PRF. The hostile way is to make abrupt changes of rate without phase continuity. It seems to me the least the cloud radar people could do is to adopt the friendly approach. Of course at a radio astronomy observatory even what is a fixed PRF at the satellite will appear as a varying frequency because of the changing range, alias the Doppler shift on the PRF. But an auxiliary antenna at the radio observatory programmed to track the transmitting satellite will have no difficulty in seeing the pulses through the sidelobes of the transmitting antenna, and will be able to lock onto the pulse train and thus generate receiver suppression pulses to be applied to the radio astronomy receivers. The phase-lock loop will have to have the ability to accommodtae the Doppler shift. Provided and deliberate changes to the PRF are phase continuous and smooth it will be able to take them in its stride. However if the cloud radar has abrupt discontinuities in its PRF then the phase-lock loop will be thrown every time, and the suppression pulses, protecting the RA receivers will occur at the wrong times and thus provide no protection until the loop recovers. If some of the satellites are already in orbit, the question as to whether they have adopted the friendly or the hostile approach must have been decided and be incorporated in the flight hardware. Do you know which way they have gone? There is also the question, which is discussed in my note, concerning a friendly shape of transmitted pulse. Do you what what has been adopted? Who is responsible for the cloud radar? I had not heard the NRAO is pulling out of Tucson. I received my copy of the "Spectrum Management for Radio Astronomy" report short time ago. Well done you and well done Murray.. I'm reading the contributions with interest. However I can't bring myself to cast my eyes over my own stuff. It always makes me feel slightly sick to see anything I've written in print. I got my thumb across the output of a 5kV power pack a few weeks ago. The pack had a trip set to about 90mA. It tripped! I attended the IAU conference on the Transit of Venus which was held at Preston just up the road for me. The weather was kind and we saw the transit which started at 0630 local time. I went down the corridor in the Hall of residence where i was staying at 0430 banging on all the door to get every one to the bus waiting to take us to the observatory. Later in the morning I sat in Much Hoole churchyard with a journalist from the the Times Higher Educational Supplement eating cream scones with strawberries at Rupert Murdoch's expense. As a result I was quoted by name in the THES. No other dramatic news. Best wishes John johnpon@supanet.com