ANDREWS. BENSON WILLIAMC. DRAEGER LAWRENCER. PETTINGER University of California* Berkeley, Calif. 94720 Ground Data Collection and Use These are essential components of an agricultural resource survey. INTRODUCTION sions based on their efforts to perform re- HE IMPORTANCE OF collecting meaningful gional agricultural inventories in Maricopa T and timely ground data for resource in- County, Arizona, using space and high-alti- ventories which employ remote sensing tech- tude aerial photography, as part of an ongoing niques is often discussed, and appropriately NASA-sponsored research project (Draeger, so. However, those wishing to conduct inven- et a]., 1970). This paper draws upon examples tories frequently fail to devote as much time from this research. However, much of the dis- to the planning of field activities which occur cussion is relevant to other disciplines for in conjunction with an aircraft mission as which ground data is important. they do in planning the flight itself. As a re- sult. adequate remote sensing data mav be collected,-but no adequate sipporting infor- Preliminary evaluation of the geographical ABSTRACT:During the past two years, extensive studies have been conducted out in the Phoenix, Arizona area to ascertain the degree to which sequential high- altitude aircraft and spacecraft imagery can contribute to operational agri- cultural crop surveys. Data collected on the ground within the test site con- stituted an essential component of the three phases of the survey: (I)farniliariza- tion with the area and design of preliminary evalz~ationexperiments, (2) train- in,g of interpreters, and (3)providing the basis upon which image interpretation estimates can be adjusted and evaluated. This paper will discuss the problems encountered when gathering extensive sequential agricultural ground data, re- quirements for such data in terms of amount and timing, methods of collecting, handling and compiling such data in a useful form, and the use of ground data in the survey evaluation process. mation is available to permit its meaningful area for which an agricultural inventory is evaluation. Unless care is taken in the speci- planned must be made in light of the capabil- fication of ground data collection efforts, the ities of available remote sensing systems. Two resulting inventory may be of minimal value. categories of information must be known for Ground data is used in all three phases of this evaluation: (1) the optimum remote sen- an agricultural resource survey. First, some sing specifications for crop discrimination and field work may be necessary in the survey identification, and (2) the sequential pattern planning stage. At this point, preliminary of crop development and the geographical evaluations are made to determine how the distribution of each crop type. If this infor- survey might best be organized. Secondly, mation is available at the beginning of the ground data must be used to train image in- planning stage, additional ground data may terpreters (both human and electronic) and to not be needed to complete the survey design. judge their competence. Finally, accurate ground However, if the available information is in- data is crucial for evaluating operational sur- adequate, certain kinds of data, both from zrey results and adjusting interpretation esti- existing records and from limited field work, mates. must be obtained. The authors have come to these conclu- Specifications for remote-sensing imagery * Forest Remote Sensing Laboratory 1159 - - 1160 PHOTOGRAMMETRIC ENGINEERING, 1971 JFMAMJJASOND......- These two particular areas were chosen for Alfalfa several reasons: (1) each was contiguous, .. .. making the collection of data within each plot Barley & Wheat .. ........- a convenient process; (2) they contained rep- Sugar Beets ------ resentative examples of each of the important Cotton .. , - - - - - - - .. .. ---- crop types grown in the Phoenix area; (3) .. planting nearly 400 separate fields were contained in -growth --- harvest the two plots, providing enough examples for FIG. 1, This crop summarizes the de- training and testing of interpreters; and (4) velopment patterns of five major crop types in the both were easily reached by vehicle so that Maricopa County test site. The duration of each they could be field checked in one day by a of the three main phases of development (planting, growth and harvest) is indicated. It was prepared two-man crew. As larger areas (or a greater using field data and published crop status reports number of areas which were for Maricopa County. This kind of information is separated) could not be investigated (eco- used to select optimum dates for discrimination of nomic constraint), little information regarding each crop type 0x1 aerial and space photography. relative distribution of crop type could be obtained. However, as stated above, the ob- are based on the objectives of the survey. The jective in selecting the two pilot plots was to specifications should consider: (1) the sensor evaluate image characteristics and relate system capabilities (camera systems, max- them to survey planning. A regional sample imum flight altitude, etc.), (2) interpretation of plots would have been taken if information procedures to be used (prints us. transparen- concerning variability of crop distribution had cies, human us. machine interpretation), (3) been desired. film-filter types and (4) resolution require- In order to ascertain optimum film-filter ments for identification of each crop type. If combinations and dates for identifying par- the factors that affect interpretation accuracy ticular crop types, air photo missions over 1 (film type, resolution, contrast, etc.) and the the test areas were flown at approximately proper time(s) of year for obtaining imagery monthly intervals, and extensive photo in- have not been determined, either from pre- terpretation tests were conducted using the vious experience with similar conditions or photography thus obtained. An essential ele- from published surveys, then some prelimi- ment in any photo interpretation testing pro- nary testingof film types and dates of imagery cedure is the collection of accurate, timely is necessary. ground data. Data concerning crop distribution and de- velopment can often be derived from current INTERPRETERTRAINING records of agricultural advisors and published The accuracy of a survey that employs re- agricultural literature and statistics, or through the actual compilation of ground data. Oneof the most useful forms for present- ing such crop development information is the crop calendar (Figure 1). For each crop type, the calendar indicates the major periods of crop development (for example, planting, growth and harvest) as they occur through the year. From such a calendar one can select the time(s) of the year for maximum discrim- ination of particular crop types based on their sequence of development relative to all other crops. For example, in the Maricopa County sur- vey, information regarding crop development patterns was not available. Therefore, two FIG.2. TWOtest sites, initially selected for study field plots-16 square miles and 22 square on space and sequential high altitude aerial pho- tographs during 1969, are outlined on this black- miles-were selected in which crop develop- and-white enlargement of a portion of Apollo 9 ment could be monitored (Figure 2). Data Infrared Ektachrome frame AS9-26-3801 of the collected from these plots at the time of photo Phoenix, Arizona area. Detailed crop information was collected for the 16-square-mile area (left) and missions were correlated with theaerial photos the 22-square-mile area (right) at the time of each to determine which dates and film-filter flight. Phoenix is in the upper left, and Mesa in the binations could best be used for the survey. center of this frame. GROUND DATA COLLECTION AND USE 1161 mote-sensing techniques depends heavily on not vary significantly whether plots were 1, the training of interpreters. In turn, the suc- 4 or even 8 square miles in size. Thus plot cess of a training effort depends completely size was determined solely on an economical on accurate ground data. Only where the basis. Based on experience, it was known that ground data is absolutely correct can the in- a plot size of 8 square miles was too large for terpreter be presented with examples repre- an adequate number to be easily ground- senting the complete range of crop variation. checked in a reasonable time period, and that In addition, once the training phase has been if the plots were only one square mile in size, completed, it may still be a difficult task for field crews would spend a disproportionate an interpreter to satisfy himself that he has time traveling between plots relative to the learned the identifying characteristics of a time spent collecting data. The decision was crop. If some of the training examples he had made to use four-square-mile plots (two miles studied were incorrectly identified initially by by two miles) because they were large enough field crews, his task becomes impossible. He to contain a representation of the major crops will believe that there is greater variability growing in the particular area where the plot within a crop type than actually exists, and was located, yet small enough that many he may also become more confused as to plots could be visited each day. Thirty-two differences between crop types. plots were chosen because this number could be completely field-checked within a two-day period by a team of three persons (economic After the basic decisions as to image type constraint), enough data would be provided and date of photography have been made, the for adequate statistical analyses (statistical next step in the preparation for an operational constraint), and all major crop types would survey is to establish permanent field plots be represented in one or more of the plots. from which data can be collected. These data The allocation of sample plots to a survey are used to determine the accuracy of the sub- area is often made more statistically efficient sequent photo interpretation estimates and if the area is stratified into relatively homo- for the later adjustment of these estimates.