Searching for California's Illicit Crop: Cannabis sativa

Richard L. Gunther
December 7, 2005
ES 771 Remote Sensing

Characteristics and Uses of Cannabis sativa

Cannibas sativa
Cannabis sativa is a flowering plant that develops into bush approximately 8 to 10 feet tall. The leaves have a distinct 5 point palmate pattern. Endemic to Central Asia this plant has spread worldwide because of its many uses.

The structural parts of the plant have a wide variety of uses. The stem contains a tough fiber that is used in the manufacture of textiles and rope. The plant's common name when referring to the fibrous stem tissue is hemp. The seeds contain a drying oil that is added during the making of varnishes, paints and soap. Finally, the leaves and flowers are used for the drugs they contain. When referring to the leaves and flowers the plant is called marijuana (Encarta,2002).

Cannabis sativa and the Law

An Illegal Marijuana Garden next to a Deciduous Forest
Cannabis sativa first became illegal to grow or possess in the United States with the passage of the Marijuana Act of 1937. The Marijuana Act was determined to be unconstitutional in 1969. As a result, the Controlled Substance Act of 1970 was passed and signed into law. Within the law Cannabis was classified as a Schedule 1 drug. Schedule 1 drugs are defined in the law as having a high potential for abuse, no current accepted medical use and lack safe use even under medical supervision (Wikipedia,2005).

At the present time, Cannabis sativa is still a Schedule 1 drug and is illegal in the United States. Several states, including California, have taken small steps in the decriminalization of marijuana. Part of this decriminalization effort surrounds the use of marijuana for medical purposes. Much debate has occurred over the medical benefits of marijuana but to this point marijuana remains an illegal drug according to federal law.

California: A Large, Fertile Ground for the Cultivation of Cannabis Plants

Cannabis sativa is an introduced species that grows quite well throughout the state. California's Mediterranean climate provides ideal conditions for the plants to flourish. Cannabis plants are planted in the spring and are harvested in the fall. As with most commercial crops grown in the state illegal Cannabis gardens need water delivered to them in the dry summer and fall months. When illegal gardens are discovered by law enforcement officials there is usually a sophisticated irrigation system in place to keep the plants well hydrated for maximum production (Snyder, 2005).

California has a land area of almost 156,000 square miles. The federal government owns roughly 45 percent of the state. This means that the federal government is responsible for monitoring an area of 70,200 square miles. This is a tremendous area to patrol by land so remote sensing from the sky should be a productive technique for law enforcement officials.

Top Ten National Forests for the Eradication of Marijuana in 2003

The map of the United States depicts the number of Cannabis plants removed from National Forests in the United States. Clearly, California's National Forests are heavily utilized for the illegal cultivation of Cannabis sativa. There are a variety of reasons why this occurs including, but not limited to, the ideal climate, remoteness of these forests, huge areas of uninhabited land and finally, the human demand for the drug.

"CAMP": A Team Effort to Erradicate Cannabis Plants in California

CAMP's Totals for 2005
The Campaign Against Marijuana Planting (CAMP) originated in 1983 by the federal government as a multi-agency task force. This force would eventually involve federal, state and local law enforcement agencies in the effort of eliminating illegal marijuana cultivation in California. The results from the 2005 season show that a considerable amount of marijuana was collected and removed from the drug market. CaGov

Currently, law enforcement uses a variety of remote sensing instruments to find marijuana plantations. All of the remote sensing devices are ground-based instruments. Magnetometers are placed along roads that lead into areas of limited recreational value. These sensors record the day and time of vehicular traffic. Seismic sensors are used to detect direction of travel. Infrared sensors record human traffic in isolated areas. In each case officers are looking for unusual patterns of travel that may lead them to illegal activities.

Finally, human observers from helicopters or airplanes are remarkably successful at picking out Cannabis gardens. The human eye is able to detect the slight differences of light reflected from Cannabis leaves and native vegetation. Simply keeping spotters airborne for a longer time periods leads to the identification and eventual erradication of more Cannabis plants.

Remote Sensing Cannabis sativa from the Sky: Research, Possibilities and Challenges

Due to the stealthy nature of law enforcement there is not much current information concerning hi-tech remote sensing of Cannabis plants available to the general public. If law enforcement officials shared the latest developments, then individuals growing the Cannabis would make every effort attempt to hide their plants.

Limited information has been made available by the United States Department of Agriculture. The following points were submitted to the Office of National Drug Control Policy from the research arm of the Department of Agriculture. (Walthall, 2003).

  • Cannabis plants possess leaf and canopy spectral reflectance patterns similar to other green plants.

  • The contrast between Cannabis and other plant canopies is highlighted in the green, red edge and near-infrared wavelengths.

  • There are more spectral differences between Cannabis and tree species than with annual plants.

  • Microscopic structures on Cannabis leaves cause specular reflectance which causes the leaves "emerald-green" color.

  • Research should take into account the efforts that growers go to in masking their crops from the sky.

    Cannabis and a Variety of Trees
    This graph shows how Cannabis' reflectance is quite distinct from a variety of trees from a deciduous forest. A comparison of trees from a California forest was not available on the World Wide Web. However, it is reasonable to assume that differences do exist between the perrenial plants of California and Cannabis. These differences could be exploited to help law enforcement spot Cannabis plantations from the sky.

    The most current development in Cannabis cultivation would render canopy analysis ineffective. During the 2005 growing season Cannabis plants were found growing underneath Chapparal vegetation. Workers had gone onto a shrubby hillside and hollowed out the understory. The upper canopy of native plants had been left intact. The Cannabis plants were growing under the natural canopy. Growing under the canopy stunted the Cannabis plants but this technique definitely masks the plants from the sky.

    Spectral Signatures of Vegetation and Soil
    Spectral signatures of vegetation and soil could be used to identify illegal plantations. A Cannabis plantation growing in a Chaparral biome could be detected based on the quantity of water in the leaves. As the Chaparral vegetation dries out in the summer and fall, the irrigated Cannabis plants would be green and full of water.

    Looking at green versus dry vegation reflectance data would certainly identify situations that were are not illegal activites. Springs, creeks and small ponds would all have green vegetation while dry vegetation would occur nearby. Water content analysis would require considerable ground truthing to develop an effective identification system.

    Spectral Signature of PVC Pipe
    Remote sensing could be used to identify manmade materials that are used for the cultivation of Cannabis plants. One unique item not expected to be found on National Forest lands is PVC pipe. PVC pipe is used in irrigation systems to keep the plants growing. PVC pipe running all over a hillside in a National Forest would certainly warrant a closer look.

    One shortcoming of this technique is that the growers could bury or cover the irrigation pipes. Masking the PVC pipe would be considerable amount of work but the financial returns from Cannabis crops is substanial.

    According to current available information there is no sky-based remote sensing of Cannabis sativa on public lands in California. Law enforcement agencies are using effective ground-based systems to locate Cannabis plants on public lands. Perhaps, in the future, more time and effort will lead to the development of sky-based remote sensing systems that will get the job done.