SEACOOS CDL v2.0 December 9, 2004 13 float wl(time) ; wl:standard_name = "water_level" ; wl:units = "m" ; wl:reference = "MLLW" ; wl:reference_to_MLLW = 0. ; wl:reference_to_MLW = 0.0589999999999999 ; wl:reference_to_MSL = 0.785 ; wl:reference_to_MTL = 0.775 ; wl:reference_to_DTL = 0.796 ; wl:reference_to_MHW = 1.492 ; wl:reference_to_MHHW = 1.593 ; wl:reference_to_NAVD88 = 0.858 ; wl:reference_to_NAVD88_benchmark_id = "KV3519" ; wl:reference_tide_datum_time_period = "January 1983 - December 2001" ; wl:reference_tide_datum_epoch = "1983-2001" ; wl:z = 0. ; The second example shows the minimum variable attributes to provide for water level data.    float wl(time) ; wl:standard_name = "water_level" ; wl:units = "m" ; wl:reference = "MLLW" ; wl:reference_to_MLLW = 0. ; wl:z = 0. ; 7.4 Ocean Currents Horizontal ocean currents require two dependent variables to describe the speed and direction of the current or the eastward and northward components. The variable attribute water_dir: reference is used to define the reference direction such as True North or Magnetic North. The variable attribute (water_spd: z and water_dir: z) gives the height of the current measurement in relation to the description and units used by the vertical variable. The examples given are for a platform and sensor where the vertical variable is constant. The first example shows how to represent current magnitude and direction (water_spd and water_dir).   float water_spd(time);   water_spd: standard_name = "current_speed"; water_spd: units = "cm s-1"; water_spd: z = 0; float water_dir(time); water_dir: standard_name = "current_to_direction"; water_dir: units = "degrees"; water_dir: reference = "clockwise from true north"; water_dir: valid_range = 0.,360.; water_dir: z = -5; The following example uses eastward and northward components (water_u and water_v).   float water_u(time, lon, lat) ; water_u:standard_name = "eastward_current" ; water_u:units = "cm s-1" ; water_u:z = -5. ; float water_v(time, lon, lat) ;