5You will need• colored pencils,• lined paper (or graph paper), and• a three-dimensional object (supplied by your teacher).1. Place an object on the floor. Look at it from directly overhead. Sketch it.This is an aerial view. Airplanes, satellites, the Space Shuttle, and the International Space Stationcan take aerial views of objects on Earth.2. Place an object on a flat desk or table top. Stand to the side of the object. You should see both the topand one or two sides of the object. Sketch it. Add perspective to capture the shape more correctly.This is an oblique view. Airplanes, satellites, the Space Shuttle, and the International Space Stationcan also take oblique views of objects on Earth.3. Kneel or sit down so you are looking directly at the side of the object. You should not see the top ofthe object. Sketch it.This is a ground-level view. Airplanes, satellites, the Space Shuttle, and the International SpaceStation do not take this type of view of Earth. It is what is typically seen by human eyes.1Module 4, Investigation 3: Log 1Gaining different perspectives62Module 4, Investigation 3: Briefing 1Background on the Petén and ground truthingThe Petén, GuatemalaThe Petén, northern Guatemala, was once inhab-ited by a population of several million Maya beforethe population collapsed in the 9th century A.D.The 7th and 8th centuries were the height of theMayan civilization; by 930 A.D. only a few scatteredhouses remained. Scientists think that at the timethe population collapsed, the Maya had deforestedmuch of their region. Now after centuries ofregrowth, the Petén is the largest tropical forest inCentral America, but once again, it is experiencingrapid deforestation as new settlers invade the area.The old sustainable techniques used by the nativepopulation are being abandoned in favor of moredestructive monoculture and cattle raising. Thesenew methods also contribute to the destruction andlooting of unrecorded archeological sites.Today remote sensing and geographic informationsystem (GIS) analysis are used to address issuesin Maya archeology as well as to monitor theeffects of deforestation. The ancient Maya suc-cessfully adapted their agricultural methods to theirenvironment, but even so, they finally overusedtheir resources. Current inhabitants are threaten-ing to do the same thing in less time with a smallerpopulation. Scientists are using remote sensingand GIS to learn from the past to protect theresources of the future, but they cannot rely only onremotely sensed data. By studying remote sensingimages of the Petén, scientists can see• different types of vegetation,• the pattern of deforestation,• Mayan roads that lead to unrecorded sites,and sometimes• archeological sites themselves.Sometimes it is necessary to go to the jungle toverify what they see in the remote sensing images.This is called ground truthing.Maya Biosphere ReserveCentral American countries have establisheddozens of national parks, including the Petén.Change-detection analysis, using satellite datafrom 1986 to 1997, shows increasing deforestation,but the large size of the forest makes it hard tomonitor and protect. Satellite imagery is proving tobe a valuable monitoring tool. The Maya BiosphereReserve was established in 1990 through anagreement between three neighboring countries,Mexico, Guatemala, and Belize. The reserverepresents the largest continuous tract of tropicalforest remaining in Central America. Besidesforest, the reserve also contains extensive, envi-ronmentally important, seasonal, freshwaterwetlands (bajos).When settlers clear and burn the rain forests foragriculture, the thin soils quickly erode, and as aresult, the flora and fauna are destroyed. Archeo-logical sites are damaged by the fires’ heat and bythe erosion. The newly cleared landscape alsomakes undiscovered archeological sites morevisible and accessible to looters. For the reasonsmentioned previously, protecting the rain forestalmost always protects the archeological sites too.Ground Truthing in the PeténGround-truth information, often referred to as“reference data,” involves the collection of mea-surements or observations about objects, areas, orphenomena that were remotely sensed. Thisground-truth information can be used by socialscientists in two ways: first, the data can aid in theinterpretation, analysis, and validation of theremotely sensed data; second, it helps in under-standing the socioeconomic forces behind human-produced, land-cover modifications.Ground truthing is expensive and time consuming.In recent years, even though the cost of computerhardware and software for remote sensing hasdropped, the costs of ground-truth activities haveincreased because airfare, lodging, vehicle rental,food, labor, and other costs have risen. Recentadvances in GPS receivers and digital data fieldrecorders have helped keep costs down becausethey make researchers much more efficient whilethey are in the field.In order to create an accurate reference data set,scientists have to visit as many sites as possible inremote and rugged Petén. Typically, they changelocations each day. They do not remain at a site orvillage to excavate archeological features—theysimply map and verify their existence. Some of thechallenges encountered by the field workersincluded logistical and communication problems,73Module 4, Investigation 3: Briefing 1Background on the Petén and ground truthingequipment failure, poor map quality, physicalstress, and unfriendly local inhabitants. Once aresearch team was captured and held at gunpointfor several hours before being released.Logistics are probably the biggest fieldwork prob-lem. Often team members are the first profession-als to visit an archeological site. A logistics coordi-nator schedules, in advance, the jeeps, boats,aircraft, mules, horses, and workers that will helpthe team get to its destination. Since many areasof the Petén do not have telephones, a Guatema-lan team member must make arrangements for therentals with local people weeks or months inadvance. The more inaccessible the location, themore difficult the arrangements. Once the logisticshave been coordinated, the field missions last twoto three weeks. As the mode of travel switchesfrom jeeps to boats to horses and mules, it iscritical that the dates, times, and locations bearranged in advance so that the vehicles, guides,and animals are there to help the team get to itsdestination.