PDS_VERSION_ID        = PDS3                                                  
RECORD_TYPE           = STREAM                                                
OBJECT                = TEXT                                                  
  PUBLICATION_DATE      = 2004-01-26                                          
  NOTE                  = "INFO.TXT describes the Electron Reflectometer      
                           (ER) data available on this volume."               
END_OBJECT            = TEXT                                                  
END                                                                           
                                                                              
The DATA/ER directory contains the Electron Reflectometer (ER) data.          
These data consist of a time ordered series of omnidirectional electron       
flux measurements from the Electron Reflectometer instrument on the Mars      
Global Surveyor (MGS) spacecraft. The ER data on this disk cover the          
period 7/15/03 - 7/22/03.                                                     
                                                                              
Within an ER data file, each record consists of a time tag with 19            
scalar data points representing measurements of the electron flux in          
19 different energy channels, ranging from about 10 eV to 20 keV, with        
an energy resolution of 25%. Each data point is a measure of the              
electron flux (cm-2 sec-1 ster-1 eV-1) averaged over a 360 x 14 degree        
disk-shaped field of view (FOV). (Parts of this FOV are masked because        
of spacecraft obstructions.) During the Science Phasing Orbits (SPO),         
the spacecraft was in Array Normal Spin (ANS) configuration, for which        
the ER field of view sweeps out the entire sky (4-pi ster) every 50           
minutes, which is much longer than the integration time per record (2 to      
48 sec, depending on energy and telemetry rate) and much longer than          
most timescales of interest in Mars' plasma environment. The ER data are      
intended to be used in conjunction with the Mars Global Surveyor              
Magnetometer (MAG) data, which provide the magnetic field vector and          
spacecraft ephemeris data as a function of time. Electrons travel along       
the magnetic field lines in tight helices (few km radius) at high speed       
(roughly one Mars diameter per second). Thus the electron data contain        
information about the plasma environment, as well as about the                
large-scale configuration of the magnetic field, which is sampled             
locally by the MAG. (The MAG data are found in the directory /DATA/MAG        
on this disk.)                                                                
                                                                              
The file naming convention for files in the DATA/ER directory is              
as follows:                                                                   
                                                                              
99067.STS is interpreted as                                                   
                                                                              
99 = year 1999                                                                
067= day of year '067'                                                        
STS= 'standard time series' format                                            
                                                                              
The detached PDS label file describing the file 99067.STS is named            
99067.LBL.                                                                    
                                                                              
Each ER data file consists of an attached ASCII text header, followed by      
an ASCII table containing 1 day of time series data. The table in each        
file has fixed-length records of length 233 bytes. Each row of data           
contains 20 columns, and is terminated by the ASCII record delimiter          
characters carriage return and line feed. Each row consists of a time         
stamp followed by 19 electron flux values. The data are provided at the       
full instrument downlink sampling frequency, which varies by orbit            
(spacecraft telemetry mode).                                                  
                                                                              
In addition to the data files, this disk contains documentation files         
which describe the datasets on the disk, the instruments from which the       
data came, and the Mars Global Surveyor spacecraft and mission. These         
files are found in the CATALOG and DOCUMENT directories, and are              
described in the files CATALOG/CATINFO.TXT and DOCUMENT/DOCINFO.TXT.          
                                                                              
This disk also contains browse plots (PostScript files) summarizing the       
ER and Magnetometer (MAG) data on the disk. These plots are contained in      
subdirectories of the BROWSE directory.                                       
                                                                              
Besides accessing ER data files directly, users with Web browsers             
can access them via links in the HTML file ERDATA.HTM in the EXTRAS           
directory. Such users also can navigate the entire disk using the             
file AAREADME.HTM in the disk root directory.