TOC |              | Next Section | INDEX |

Tutorial: Static Baseline Processing Using run_survey

INTRODUCTION

Estimating more accurate coordinates for a site is a primary purpose of this software suite. More specifically, run_survey can generate estimates of static site coordinates referenced to other sites and the GPS satellites whose coordinates are tightly constrained. Local jargon calls this "baseline processing with fixed sites and orbits.' The double-differenced phase observable is used; the psuedorange effectively ignored. Double-differencing, by definition, implies that minimally, data from two sites must be processed. The maximum number of sites is set by parameter in the software code and system resources, but 55 is common. In addition to site coordinates, double-difference phase biases and corrections to a tropo model will be estimted.

The programs and scripts have considerable flexibility in how this processing is done, but experience has shown that a basic strategy for initial processing is useful and thus the run_survey script was born. From this basic processing, manual processing can begin or specialized processing designed with the added confidence of a standard starting point. In most cases, however, no additional processing will be necessary.

A general description of this task would include:

  1. creating a work area,
  2. downloading the data,
  3. selecting an ephemeris,
  4. selecting a site or sites to hold fixed,
  5. creating the POM files,
  6. running run_survey,
  7. evaluating the results,
  8. and manually modifying the processing if necessary.

The following sections describe each of these steps in the form of a tutorial. Note that the data and initial files needed can be downloaded from the distribution site for the run_survey software. A description of this process is given below. This is necessary because the data distribution sites keep only the most recent data on-line (for very practical space reasons) and so these tutorials will rapidly become obsolete. Consider the sections describing downloading files, steps 2 and 3 above, as purely as generic examples and follow them substituting dates and file names as appropriate. However, for the tutorial, replace these steps with the description given below.

Conventions used in these tutorials

The tutorials are written like a "cook book", i.e. showing each step required to accomplish the task. These commands you, the user, would type are shown indented and in bold. Responses from the system are also indented but in the normal font. Interspersed are comments identifying each task, often with some explanatory information. These comments are not indented.

NOTE: Data distribution centers are continually archiving and removing older data thereby making room for newer files. As a result, the files mentioned in this tutorial are almost certainly not on-line at the distribution centers. However, the files used in the tutorial are available through the software distribution site and the guide for retrieving them follows. Please use the commands shown below to down-load the required files rather than those given in Sections 2 and 3 of the tutorial. In turn, use Sections 2 and 3 as generic examples of down-loading files from distribution centers.

NOTE: This tutorial is written for a Unix environment and carries an assumption that the user has a basic familiarity with this envirnoment. A basic understanding of the Global Positioning System and its jargon is also assumed.

Downloading Data, Nav And Ephemeris Files From The Distribution Site

Description

The data, navigation message and ephemeris files used in the tutorials are available via anonymous FTP from the software distribution site. Once there, simply click on each of the files listed. Your web browser should pop open a window allowing you to download each file. The tutorial below describes an alternate means of download these files using FTP.

Tutorial

The responses from the FTP site may vary with site but should be similar to and understandable from the example. Some descriptive notes follow the example.

Notes

If the site address fails, you may need to use the site's IP address. For example, one could use

in place of

The anonymous FTP sites use the guests name and address, me@my.home.address in the example above, so make the appropriate substitution. 

 TOC |              | Next Section | INDEX |

bl_howto.html
January 14, 2000