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Radar Observing Advice

Introduction

The GBT sometimes participates in radar experiments with either Arecibo or Goldstone. Radar projects have included the planets Mercury, Venus, Mars, near-Earth asteroids, the rings and satellites of Saturn. There are only a few radar astronomers, and most of them are very familiar with how to observe with the GBT. But sometimes a student is sent, who needs more help. Also the radar back end (or "pfs") requires cabling to be done by hand so if an observer is running remotely, he may need one of us to change or check the cabling.

Prior to each radar run, GBT people need to check that the reference signals and IFs are properly connected at the right power levels. If necessary, we should advise the observer on Astrid configurations and observing scripts. We do not deal with operating the pfs; the radar observer takes care of that part.

Observing Frequencies used: P-band (430 MHz), S-band (2380 MHz), or X-band (8560 MHz). Arecibo can transmit at P- or S-band, and Goldstone can transmit at X-band.

The Radar Back End ("pfs") and hardware connections.

The radar data acquisition rack is located in the GBT equipment room to the immediate right of the converter filter rack.

A general description of the PFS ("Portable Fast Sampler") and some radar results obtained with it may be found at Jean-Luc's Sampler page. Also one may find hardware and software information. There is also a paper about the pfs in Proc. 2002 URSI Gen. Assembly, Maastricht, August 2002.

The pfs needs the following signals from the GBT system:
• 2 IF signals, routed from Converter Modules 10 and 14 (good CM power levels are 4 to 5v )
  • typical IF power levels at the input to the radar downconverter are -33 dbm with 80 MHz bandwidth.
• 10 MHz reference (+13dbm)
• 1 pps reference
• 750 MHz LO at +13dbm (from NRAO-supplied HP656B synthesizer)
• sometimes an additional reference signal at 1 or 5 MHz is needed, provided by an external NRAO-supplied synthesizer.

In the pfs rack there are two computers, pfs1 and pfs2. There are two sampler chassis also called pfs1 and pfs2, controlled by the similarly named computer. Jean-Luc has written a Brief Users Guide for the PFS, which explains how to program the pfs for data acquisition and display of data statistics and spectra.

• The modules in the pfs rack are as follows, from top to bottom:
  • pfs1 computer
  • Down converter:
    • the left IF input (A) comes from Converter Module 10, J4, centered at 720 MHz.
    • the right IF input (B) comes from Converter Module 14, J4, centered at 720 MHz.
    • The LO input comes from an external synthesizer (HP656B) at 750 MHz.
  • Baseband mixer
  • Filter module
  • pfs1 sampler module (needs 1pps signal input)
  • LO distrubution (needs 10 MHz reference input)
  • pfs2 sampler module (also needs 1pps signal input)
  • pfs2 computer.
• PFS Cabling Instructions
• For Jean-Luc's Mercury Observations, usually a planning page is set up for reference:
  • Jean-Luc's planning page for Mercury radar
• Data files, typically 10s of GBytes in size, are stored on external disks attached to the pfs1 or pfs2 computers. The users may take their data disk home, or write the data onto a tape backup. GBT friends generally do not need to worry about the data management. The radar users take care of it.

Astrid Configurations and scripts

• Astrid scripts for Radar observing are usually kept in the directory /home/astro-util/radar/

• Catalogs and moving source specifications -- refer to Astrid Catalogs
  • For moving objects, one may use Ephemeris Tables
  • One may just give the planet name as the Location in a Scan Type command, such as "Mercury", "Mars", etc., but one must at least invoke the Astrid Catalog software with some Catalog command. The minimum is "Catalog(None)"

• Examples for Mercury radar observing.
  • Configuration: /home/astro-util/radar/merc_Apr08/Mercury_Xsetup.py

# Example Astrid setup script for observing Mercury # project 06B49, Jun 2006 # also project 08A_069, April 2008 # configuration - 2 kHz offset from nominal 8560 MHz Vsetup = """ receiver = 'Rcvr8_10' obstype = 'Radar' backend = 'Radar' nwin = 1 restfreq = 8560 deltafreq = -0.002 bandwidth = 20 swmode = "tp_nocal" swper = 0.2 swfreq = 0.0, 0.0 tint = 0.2 vlow = 0 vhigh = 0 vframe = "topo" vdef = "Radio" noisecal = "lo" pol = "Circular" """ Catalog(None) # dummy source catalog (needed so "Mercury" is understood)

• • Typical scheduling block for Mercury

# Astrid script for observing Mercury # project AGBT08A_069 # # read config from file execfile("/home/astro-util/radar/merc_Apr08/Mercury_Xsetup.py") Configure(Vsetup) # move to Mercury Slew("Mercury") # peak and focus on a nearby calibrator AutoPeakFocus(None, None, 8560.0) Break("Check the peak/focus") # peak on Mercury : 20' scans Peak("Mercury", Offset("Encoder",0.333,0), Offset("Encoder",0,0.333), 30, "1") Break("Check the peak") # configure for radar and adjust levels on Mercury Configure(Vsetup) SetValues("ConverterRack", { 'CMAttenuator10' : 3, 'CMAttenuator14':6 } ) Slew("Mercury") Balance() Break("Here we may have to adjust power levels manually") #all is ready now, so track Mercury for 2.5 hours Track("Mercury", None, 8000, "1") # alternately, track until specific UT time: Track("Mercury", None, None, "1", stoptime="17:45:00")

• Examples for Lunar mapping.
  • Configuration: /home/astro-util/radar/moon_june08/lunasetup2.py :

# Configurations for Lunar radar # # 430 MHz setup # c430 = """ receiver = 'Rcvr_450' obstype = 'Radar' backend = 'Radar' nwin = 1 restfreq = 430.000006 deltafreq = 0 bandwidth = 40 swmode = "tp_nocal" swper = 1.0 swfreq = 0.0, 0.0 tint = 30 vlow = 0 vhigh = 0 vframe = "topo" vdef = "Radio" noisecal = "off" pol = "Circular" """ # function for setting attenuators # def c430atten() : pfattens = {'ifChannelCAttenuator':12, 'ifChannelDAttenuator':12 } SetValues("RcvrPF_1", pfattens) cmattens = { 'CMAttenuator10':2, 'CMAttenuator14':16 } SetValues("ConverterRack", cmattens) # Radar Observing at S-band (2380 MHz) c2380 = """ receiver = 'Rcvr2_3' obstype = 'Radar' backend = 'Radar' nwin = 1 restfreq = 2405 # note: set LO2=15810 (conv modules 10 & 14) # so that 2380 MHz converts to 720 at the inputs to the PFS. # Rest freq is set to 2410 so that IF Rack 80 MHz bandpass filter # helps cut down the satellite audio channel (at about 2340 MHz) bandwidth = 80 swmode = "tp_nocal" swper = 0.2 swfreq = 0.0, 0.0 tint = 0.2 vlow = 0 vhigh = 0 vframe = "topo" vdef = "Radio" noisecal = "off" pol = "Circular" lo2freq = 15805 iftarget=2 """

• • Excerpt of ephemeris table for a region of the Moon

# -------------------------------- # Moon Fermi FORMAT=EPHEMERIS COORDMODE=GAPPT NAME=Moon_Fermi HEAD= DATE UTC RA DEC 2008-05-01 12:03:00 23:10:29.26 -04:01:15.8 2008-05-01 12:04:00 23:10:30.60 -04:01:00.1 2008-05-01 12:05:00 23:10:31.93 -04:00:44.4 2008-05-01 12:06:00 23:10:33.27 -04:00:28.7 2008-05-01 12:07:00 23:10:34.60 -04:00:13.0 2008-05-01 12:08:00 23:10:35.94 -03:59:57.3 2008-05-01 12:09:00 23:10:37.27 -03:59:41.5

• • Scheduling Block for 430 MHz observation.

# astrid script for observing at 430 MHz # import the config definitions # execfile("/home/astro-util/radar/moon_may08/lunasetups2.py") # access the ephemeris tables for P-band Catalog("/home/astro-util/radar/moon_may08/moon.srpm.pointing.GBT") Catalog("/home/astro-util/radar/moon_may08/moon.Fermi.pointing.GBT") Catalog("/home/astro-util/radar/moon_may08/moon.Aston.pointing.GBT") Catalog("/home/astro-util/radar/moon_may08/moon.Pythag.pointing.GBT") # initial config at P-band Configure(c430) Slew("Moon") # set attenuators if desired c430atten() # or let the system set levels automatically Balance() Track( "Moon_Fermi", None, 12000)

• • Scheduling Block for 2380 MHz observation.

# astrid script for observing at 2380 MHz # import the config definitions # execfile("/home/astro-util/radar/moon_june08/lunasetups2.py") # access the ephemeris tables for S-band Catalog("/home/astro-util/radar/moon_june08/moon.Haus1.pointing.GBT") Catalog("/home/astro-util/radar/moon_june08/moon.Haus2.pointing.GBT") --- # initial config at S-band Configure(c2380) Slew("Moon") # let the system set levels automatically Balance() Track( "Moon_Haus1", None, 7200)

-- FrankGhigo - 03 Jul 2008