Horizontal and vertical controls generated by land   (geodetic)   surveys   provide   coordinated position  data  for  all  surveyors.  It  is  therefore necessary  that  these  types  of  surveys  use  first- order  and  second-order  accuracies. Hydrographic  Surveys HYDROGRAPHIC  SURVEYS  are  made  to acquire   data   required   to   chart   and/or   map shorelines and bottom depths of streams, rivers, lakes,  reservoirs,  and  other  larger  bodies  of  water. This type of survey is also of general importance to   navigation   and   to   development   of   water resources  for  flood  control,  irrigation,  electrical power,  and  water  supply. As in other special surveys, several different types  of  electronic  and  radio-acoustical  instru- ments  are  used  in  hydrographic  surveys.  These special  devices  are  commonly  used  in  determining water  depths  and  location  of  objects  on  the bottom by a method called taking SOUNDINGS. Soundings   are   taken   by   measuring   the   time required  for  sound  to  travel  downward  and  be reflected  back  to  a  receiver  aboard  a  vessel. TYPES  OF  SURVEYING OPERATIONS The practice of surveying actually boils down to fieldwork and office work. The FIELDWORK consists   of   taking   measurements,   collecting engineering   data,   and   testing   materials.   The OFFICE  WORK  includes  taking  care  of  the computation and drawing the necessary informa- tion  for  the  purpose  of  the  survey. FIELDWORK FIELDWORK is of primary importance in all types  of  surveys.  To  be  a  skilled  surveyor,  you must spend a certain amount of time in the field to acquire needed experience. The study of this training manual will enable you to understand the underlying theory of surveying, the instruments and  their  uses,  and  the  surveying  methods. However,  a  high  degree  of  proficiency  in  actual surveying,  as  in  other  professions,  depends  largely upon the duration, extent, and variation of your actual experience. You should develop the habit of STUDYING the  problem  thoroughly  before  going  into  the field, You should know exactly what is to be done; how  you  will  do  it;  why  you  prefer  a  certain approach over other possible solutions; and what instruments  and  materials  you  will  need  to accomplish  the  project. It  is  essential  that  you  develop  SPEED and   CONSISTENT   ACCURACY   in   all   your fieldwork. This means that you will need practice in handling the instruments, taking observations and keeping field notes, and planning systematic moves. It is important that you also develop the habit of  CORRECTNESS.  You  should  not  accept  any measurement   as   correct   without   verification. Verification,   as   much   as   possible,   should   be different   from   the   original   method   used   in measurement. The precision of measurement must be  consistent  with  the  accepted  standard  for  a particular  purpose  of  the  survey. Fieldwork also includes adjusting the instru- ments  and  caring  for  field  equipment.  Do  not attempt  to  adjust  any  instrument  unless  you understand  the  workings  or  functions  of  its  parts. Adjustment of instruments in the early stages of your  career  requires  close  supervision  from  a senior  EA. Collection of Engineering Data The  collection  of  ENGINEERING  DATA  is a  part  of  SEABEE  surveying.  Engineering  data is  actually  any  information  that  is  essential  for efficient  construction.  Most  of  your  fieldwork, such as running a traverse, leveling, and determin- ing   cuts   and   fills,   may   be   classified   under this   category.   However,   compiling   these   field measurements and converting them into a com- mon medium that will be of value to the engineer requires skill that can only be attained through long   experience.   Although  the  planning  and organization  will  generally  be  handled  by  the engineering officer or by a senior EA, the actual collection  of  engineering  data  will  generally  be delegated to you; hence, it is to your advantage to understand the procedures early in your career. This job may take a combination of fieldwork and office  work.  If  the  same  quality  of  the  desired information  can  be  found  from  sources  other  than actual fieldwork, do not hesitate to use them; if necessary, use spot checks to verify certain points, depending  upon  the  source. Each project requires the study of a different set  of  engineering  data,  so  it  is  up  to  the engineering officer or the senior EAs to devise a workable  method  of  compilation  that  will  suit each  particular  project.  It  is  essential  that  the compiled  data  be  complete  in  all  respects  as 11-4