I. Comprehension questions:

l.What problems can DGPS solve? 2. What is DGPS based on? 3. Where is base receiver located? 4. How many satellites are tracked in DGPS? 5. What receivers are used in DGPS method? 6. How are DGPS errors eliminated? 7. What is inverse DGPS?

2. Speak about fundamental principles of DGPS

3. Give a short summary of the text.

UNIT 8

Text В. Earth's structure /. Read aloud and memorize the following words;

average (v) - дорівнювати в середньому

call (v) - називати

consist of- складатися з

dense - щільний

dig - копати

estimate (v) - підраховувати

extremely - надзвичайно

//. Expressions for the text comprehension:

earth's crust - земна кора

flexible mantle - гнучка мантія

hot material - гарячий матеріал

in between - між ними

iron-nickel core - залізно-нікелеве ядро

land area - земна площа

Earth's structure

Earth consists of three major layers or zones - a dense iron-nickel core, a surface crust and a flexible mantle in between. The thickness of earth's crust varies. Earth's crust is thickest where there are continents - the major land areas of earth - and averages about 40 kilometers in thickness. Under the oceans where it does not support huge land-masses the crust averages only about eight kilometers in thickness.

Earth's second layer called the mantle is made of mostly extremely hot material that can flow under pressure. Digging through it would be quite a task. The mantle is 2.900 kilometers thick. Temperatures vary from 870°C near the top of the mantle to 3000°C at the bottom. The closer to earth's centre, the higher the temperatures and pressure. The layer beneath the mantle is even hotter. In the outer liquid iron core which is about 2.250 kilometers thick temeperatures can reach6.100°C.

Inside this intensely hot outer core is the inner solid iron and nickel core - the hottest part. Scientists estimate that temperatures in the inner solid core may be as high as 7.000°C.

Assignments

1. Comprehension questions:

1.Of what layers does earth consist? 2. Does the thickness of earth's crust vary? 3.Where is earth's crust thickest? 4. How thick is earth's crust under oceans? 5. What is the thickness of the mantle? 6. How does the temperature of the mantle vary? 7. What is the temperature of the inner solid core? 8. What does the inner core consist of?

2. Speak about:

a) earth's crust, b) the mantle, c) earth's core.

flow - текти

inner - внутрішній

intensely - надзвичайно

outer - зовнішній

reach - досягати

the ... the - чим ..., тим ...

thickness - товщина

liquid iron core - рідинне залізне ядро major layer - найважливіший шар solid core - тверде ядро surface crust - поверхнева кора

3. (їіує a short summary of the text.

UNIT 9

Техт В. Errors in base line measurements

/. Read a nil memorize the following words;

alone - лише, виключно, тільки

blow (v) - дути

carefully - дбайливо, уважно

duration - тривалість

effect (n) - вплив, дія

even though - навіть хоча

gradient - градієнт, ухил, схил

greatly - в значній мірі

handle (v) - обходитись

highway - шосе

hence - звідси

introduce - ввести

length - довжина

nearly - майже

negligible - незначний

permit (v) - дозволити, допустити

precise - точний

railroad - залізна дорога

readily - легко

render - зробити

sag (n) - осідання, прогин, обвисання

season - сезон

similar - подібний

source - джерело

standardize - стандартизувати

sufficiently - достатньо

experience - досвід

//. Expressions for the text comprehension:

adjacent posts - суміжвні, прилеглі

пункти, вішки

approximate formula - наближена формула

as follows - наступним чином

base line - базис, базисна лінія

bureau of standards - бюро стандартів

changes in length - зміни в довжині

cloudy days - хмарні дні

difference in elevation - різниш у висоті

favourable conditions - сприятливі умови

field season - польовий сезон

invar tape - інварна мірна лінія

lateral displacement - бокове переміщення

linear measurements - лінійні вшіри

mean temperature - середня температура

normal to - перпендикулярно

profile levels - профільні рівні

source of errors - джерело помилок

steeper grade - крутіший ухил

supporting surface - підтримуюча

поверхня

tape length - довжина стрічки

throughout the length- по всій довжині

total probable error - загальна ймовірна

помилка

unsupported portions - непідтримані

частини

up to - до

variations in temperature - коливання

температури

Errors in base line measurements

1. Tape Non-Standard Length. If the tape is carefully handled the comparison made by the bureau of standards will be sufficiently precise to render the error from.this source negligible for the duration of a field season. Experience has shown that tape changes in length over period of years even though it is not used, hence, a tape should be standardized in the same season in which it is lied.

2. Variations in temperature. The effect of temperature is the most serious source of errors in precise linear measurements.

For example, an error of 0.5° F in the temperature of a steel tape introduces an error of 1/300,000 in the measured length, which alone is greater than the total probable error permitted

in precise work. The magnitude of the error due to variations in temperature is greatly reduced by the use of an invar tape.

Favourabie conditions are those in which the air and the ground are at nearly the same temperature. These conditions are obtained on cloudy days or at night, and it is at such times that important base lines are usually measured.

3 Tape not horizontal. This .source of error is rendered negligible as follows: the difference in elevation of adjacent posts is determined by a line of profile levels run with a transit or an engineer's level. The gradient for each tape length is then readily computed.

The corrections for grades up to 5 per cent may be computed by the approximate formula.

Steeper grades may be used if necessary, but the corrections should then be computed by the exact formula. The same correction is applied to measurements of base lines along highway or railroad, the grade of the supporting .surface being obtained by levelling.

4. Wind. If a strong wind is blowing normal to the base line and if the tape is not supported throughout its length there will be a lateral displacement of the unsupported portions of the tape, thus producing an effect similar to that of a sag.

Assignments

1. Comprehension questions,:

l.Does the tape change over the period of time? 2. Who checks up tape standard? 3. What is the most serious source of errors in linear measurements? 4. How is the temperature error reduced? 5. What are favourable conditions lor the tape? 6. When is the exact formula used for correction in grade? 7. When does the lateral displacement of tape occur?